• Donald H. (Donnie) Pinkston, III's avatar
    Documents and code changes for Assignment 3 · c7b4e8f9
    Donald H. (Donnie) Pinkston, III authored
    The design document and information document are included under the doc
    directory now.
    
    Added a lot of documentation, particularly to the Schema class.
    
    Made a few changes to the ArithmeticOperator and BooleanOperator
    classes' simplify() methods so that we can do some basic
    simplifications.
    
    Added the StatisticsUpdater so that it's easier for students to modify
    statistics based on selection predicates.
    
    Fixed a bug in SelectClause where ORDER BY clauses were using the
    FROM-clause schema rather than the SELECT-clause schema.
    c7b4e8f9
Schema.java 34.9 KB
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package edu.caltech.nanodb.relations;


import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.SortedMap;
import java.util.TreeMap;

import edu.caltech.nanodb.expressions.ColumnName;
import edu.caltech.nanodb.storage.TableException;


/**
 * <p>
 * A schema is an ordered collection of column names and associated types.
 * </p>
 * <p>
 * Many different entities in the database code can have schema associated
 * with them.  Both tables and tuples have schemas, for obvious reasons.
 * <tt>SELECT</tt> and <tt>FROM</tt> clauses also have schemas, used by the
 * database engine to verify the semantics of database queries.  Finally,
 * relational algebra plan nodes also have schemas, which specify the kinds of
 * tuples that they generate.
 * </p>
 */
public class Schema implements Serializable, Iterable<ColumnInfo> {

    //========================================================================
    // STATIC HELPER CLASSES

    /**
     * This helper class is used for the internal hashed column structure, so
     * that we can do fast lookups based on table names and column names.
     */
    private static class IndexedColumnInfo implements Serializable {
        /** The index in the schema that the column appears at. */
        public int colIndex;

        /** The details of the column at the stored index. */
        public ColumnInfo colInfo;

        /** Stores the specified index and column-info value. */
        IndexedColumnInfo(int colIndex, ColumnInfo colInfo) {
            if (colInfo == null)
                throw new NullPointerException("colInfo cannot be null");

            if (colIndex < 0) {
                throw new IllegalArgumentException("colIndex must be >= 0; got " +
                    colIndex);
            }

            this.colIndex = colIndex;
            this.colInfo = colInfo;
        }
    }


    //========================================================================
    // INSTANCE FIELDS


    /**
     * The collection of the column-info objects describing the columns in the
     * schema.
     */
    private ArrayList<ColumnInfo> columnInfos = new ArrayList<>();


    /**
     * A mapping that provides fast lookups for columns based on table name and
     * column name.  The outer hash-map has table names for keys; "no table" is
     * indicated with a <code>null</code> key, which {@link java.util.HashMap}
     * supports.  The inner hash-map has column names for keys, and maps to
     * column information objects.
     */
    private HashMap<String, HashMap<String, IndexedColumnInfo>>
        colsHashedByTable = new HashMap<>();


    /**
     * A mapping that provides fast lookups for columns based only on column
     * name.  Because multiple columns could have the same column name (but
     * different table names) in a single schema, the values in the mapping are
     * lists.
     */
    private HashMap<String, ArrayList<IndexedColumnInfo>> colsHashedByColumn =
        new HashMap<>();


    /**
     * A set recording the indexes of the columns have NOT NULL constraints
     * on them.
     */
    private HashSet<Integer> notNullCols = new HashSet<>();


    /**
     * A collection of all candidate-key objects specifying the sets of
     * columns that comprise candidate keys on this table.  One of these keys
     * may be specified as the primary key.
     */
    private ArrayList<KeyColumnRefs> candidateKeys = new ArrayList<>();


    /**
     * A collection of foreign-key objects specifying other tables that this
     * table references.
     */
    private ArrayList<ForeignKeyColumnRefs> foreignKeys = new ArrayList<>();


    /** A set of the tables that reference this table. */
    private HashSet<String> referencingTables = new HashSet<>();


    /**
     * This collection provides easy access to all the indexes defined on this
     * table, including those for candidate keys and the primary key.
     */
    private HashMap<String, IndexColumnRefs> indexes = new HashMap<>();


    //========================================================================
    // INSTANCE METHODS


    /** Construct an empty schema. */
    public Schema() {
    }


    /**
     * Construct a schema whose columns are taken from the specified iterable.
     * Note that this does not work with arrays of column-info objects.
     */
    public Schema(Iterable<ColumnInfo> colInfos) throws SchemaNameException {
        for (ColumnInfo i : colInfos)
            addColumnInfo(i);
    }


    /**
     * Construct a schema containing the specified array of column-info
     * objects.
     */
    public Schema(ColumnInfo... colInfos) throws SchemaNameException {
        for (ColumnInfo i : colInfos)
            addColumnInfo(i);
    }


    /**
     * <p>
     * Create a schema that is the concatenation of one or more other schemas.
     * Schemas are copied in the order they are given.  If a column name
     * appears multiple times in the input, an exception will be generated.
     * </p>
     * <p>
     * Keys will not be copied by this constructor.
     * </p>
     *
     * @param schemas one or more schema objects to copy into this schema
     */
    public Schema(Schema... schemas) {
        this();
        for (Schema s : schemas)
            append(s);
    }


    /**
     * Returns the number of columns in the schema.
     *
     * @return the number of columns in the schema.
     */
    public int numColumns() {
        return columnInfos.size();
    }


    /**
     * Returns the <tt>ColumnInfo</tt> object describing the column at the
     * specified index.  Column indexes are numbered from 0.
     *
     * @param i the index to retrieve the column-info for
     *
     * @return the <tt>ColumnInfo</tt> object describing the name and type of
     *         the column
     */
    public ColumnInfo getColumnInfo(int i) {
        return columnInfos.get(i);
    }


    /**
     * Returns an unmodifiable list of all the columns in the schema
     *
     * @return an unmodifiable list of all the columns in the schema
     */
    public List<ColumnInfo> getColumnInfos() {
        return Collections.unmodifiableList(columnInfos);
    }


    /**
     * Constructs and returns a list of {@link ColumnInfo} objects for the
     * columns at the specified indexes.  This method can be useful with
     * {@link ColumnRefs} objects,to retrieve the columns referenced by a key.
     *
     * @param colIndexes an array of zero-based column indexes to retrieve
     * @return a list of {@code ColumnInfo} objects for the specified columns
     */
    public ArrayList<ColumnInfo> getColumnInfos(int[] colIndexes) {
        ArrayList<ColumnInfo> result = new ArrayList<>(colIndexes.length);

        for (int colIndex : colIndexes)
            result.add(getColumnInfo(colIndex));

        return result;
    }


    /**
     * Provides support for iteration over the columns in the schema.
     *
     * @return an iterator over the columns in this schema.
     */
    @Override
    public Iterator<ColumnInfo> iterator() {
        return Collections.unmodifiableList(columnInfos).iterator();
    }


    /**
     * Add a column to the schema.
     *
     * @param colInfo the name and type of the column being added to the
     *        schema
     * @return the zero-based index of the column in the schema
     *
     * @throws IllegalArgumentException if {@code colInfo} is {@code null}
     */
    public int addColumnInfo(ColumnInfo colInfo) {
        if (colInfo == null)
            throw new NullPointerException("colInfo cannot be null");

        String colName = colInfo.getName();
        String tblName = colInfo.getTableName();

        // Check the hashed-columns structure to see if this column already
        // appears in the schema.

        HashMap<String, IndexedColumnInfo> colMap = colsHashedByTable.get(tblName);
        if (colMap != null && colMap.containsKey(colName)) {
            throw new SchemaNameException("Specified column " + colInfo +
            " is a duplicate of an existing column.");
        }

        int colIndex = columnInfos.size();
        columnInfos.add(colInfo);

        IndexedColumnInfo indexedColInfo = new IndexedColumnInfo(colIndex, colInfo);

        // Update the hashed-columns structures for fast/easy lookup.

        if (colMap == null) {
            colMap = new HashMap<>();
            colsHashedByTable.put(tblName, colMap);
        }
        colMap.put(colName, indexedColInfo);

        ArrayList<IndexedColumnInfo> colList =
            colsHashedByColumn.computeIfAbsent(colName, k -> new ArrayList<>());
        colList.add(indexedColInfo);

        // Finally, return the index.

        return colIndex;
    }


    /**
     * Append another schema to this schema.
     *
     * @throws SchemaNameException if any of the input column-info objects
     *         overlap the names of columns already in the schema.
     */
    public void append(Schema s) throws SchemaNameException {
        for (ColumnInfo colInfo : s)
             addColumnInfo(colInfo);
    }


    /**
     * Returns a set containing all table names that appear in this schema.
     * Note that this may include {@code null} if there are columns with no
     * table name specified!
     */
    public Set<String> getTableNames() {
        return Collections.unmodifiableSet(colsHashedByTable.keySet());
    }


    /**
     * This helper method returns the names of all tables that appear in both
     * this schema and the specified schema.  Note that not all columns of a
     * given table must be present for the table to be included in the result;
     * there just has to be at least one column from the table in both schemas
     * for it to be included in the result.
     *
     * @param s the other schema to compare this schema to
     * @return a set containing the names of all tables that appear in both
     *         schemas
     */
    public Set<String> getCommonTableNames(Schema s) {
        HashSet<String> shared = new HashSet<>(colsHashedByTable.keySet());

        // If there are columns without a table name, null will be in the set.
        // Remove it, since that's a bit confusing.
        shared.remove(null);

        shared.retainAll(s.getTableNames());
        return shared;
    }


    /**
     * Returns a set containing all column names that appear in this schema.
     * Note that a column-name may be used by multiple columns, if it is
     * associated with multiple table names in this schema.
     *
     * @return a set containing all column names that appear in this schema.
     */
    public Set<String> getColumnNames() {
        return Collections.unmodifiableSet(colsHashedByColumn.keySet());
    }


    /**
     * Returns the names of columns that are common between this schema and the
     * specified schema.  This kind of operation is mainly used for resolving
     * <tt>NATURAL</tt> joins.
     *
     * @param s the schema to compare to this schema
     * @return a set of the common column names
     */
    public Set<String> getCommonColumnNames(Schema s) {
        HashSet<String> shared = new HashSet<>(colsHashedByColumn.keySet());
        shared.retainAll(s.getColumnNames());
        return shared;
    }


    /**
     * Returns the number of columns that have the specified column name.  Note
     * that multiple columns can have the same column name but different table
     * names.
     *
     * @param colName the column name to return the count for
     * @return the number of columns with the specified column name
     */
    public int numColumnsWithName(String colName) {
        ArrayList<IndexedColumnInfo> list = colsHashedByColumn.get(colName);
        if (list != null)
            return list.size();

        return 0;
    }


    /**
     * This helper method returns true if this schema contains any columns with
     * the same column name but different table names.  If so, the schema is not
     * valid for use on one side of a <tt>NATURAL</tt> join.
     *
     * @return true if the schema has multiple columns with the same column name
     *         but different table names, or false otherwise.
     */
    public boolean hasMultipleColumnsWithSameName() {
        for (String cName : colsHashedByColumn.keySet()) {
            if (colsHashedByColumn.get(cName).size() > 1)
                return true;
        }
        return false;
    }


    /**
     * Presuming that exactly one column has the specified name, this method
     * returns the column information for that column name.
     *
     * @param colName the name of the column to retrieve the information for
     *
     * @return the column information for the specified column
     *
     * @throws SchemaNameException if the specified column name doesn't appear
     *         in this schema, or if it appears multiple times
     */
    public ColumnInfo getColumnInfo(String colName) {
        ArrayList<IndexedColumnInfo> list = colsHashedByColumn.get(colName);
        if (list == null || list.size() == 0)
            throw new SchemaNameException("No columns with name " + colName);

        if (list.size() > 1)
            throw new SchemaNameException("Multiple columns with name " + colName);

        return list.get(0).colInfo;
    }


    /**
     * This method iterates through all columns in the schema, setting them
     * to all have the specified table name.  An exception will be thrown if
     * the result would be an invalid schema with duplicate column names; in
     * this case, the schema object will remain unchanged.
     *
     * @throws SchemaNameException if the schema contains columns with the
     *         same column name but different table names.  In this case,
     *         resetting the table name will produce an invalid schema with
     *         ambiguous column names.
     *
     * @design (donnie) At present, this method does this by replacing each
     *         {@link ColumnInfo} object with a new object with updated
     *         information.  This is because {@code ColumnInfo} is immutable.
     */
    public void setTableName(String tableName) throws SchemaNameException {
        // First, verify that overriding the table names will not produce
        // multiple ambiguous column names.
        ArrayList<String> duplicateNames = null;

        for (Map.Entry<String, ArrayList<IndexedColumnInfo>> entry :
             colsHashedByColumn.entrySet()) {

            if (entry.getValue().size() > 1) {
                if (duplicateNames == null)
                    duplicateNames = new ArrayList<>();

                duplicateNames.add(entry.getKey());
            }
        }

        if (duplicateNames != null) {
            throw new SchemaNameException("Overriding table-name to \"" +
                tableName + "\" would produce ambiguous columns:  " +
                duplicateNames);
        }

        // If we get here, we know that we can safely override the table name for
        // all columns.

        ArrayList<ColumnInfo> oldColInfos = columnInfos;

        columnInfos = new ArrayList<>();
        colsHashedByTable = new HashMap<>();
        colsHashedByColumn = new HashMap<>();

        // Iterate over the columns in the same order as they were in originally.
        // For each one, override the table name, then use addColumnInfo() to
        // properly update the internal hash structure.

        for (ColumnInfo colInfo : oldColInfos) {
            ColumnInfo newColInfo =
                new ColumnInfo(colInfo.getName(), tableName, colInfo.getType());

            addColumnInfo(newColInfo);
        }
    }


    /**
     * Finds the index of the specified column in this schema, or returns -1
     * if the schema contains no column of the specified name.  The
     * column-name object is not required to specify a table name; however, if
     * the table name is unspecified and the column name is ambiguous then an
     * exception will be thrown.
     *
     * @param colName column-name object to use for looking up the column in
     *        the schema
     *
     * @return the zero-based index of the column, or -1 if the schema does
     *         not contain a column of the specified name.
     *
     * @throws IllegalArgumentException if {@code colName} is {@code null}
     * @throws SchemaNameException if {@code colName} doesn't specify a table
     *         name, and multiple columns have the specified column name
     */
    public int getColumnIndex(ColumnName colName) {
        if (colName == null)
            throw new IllegalArgumentException("colInfo cannot be null");

        if (colName.isColumnWildcard())
            throw new IllegalArgumentException("colName cannot be a wildcard");

        return getColumnIndex(colName.getTableName(), colName.getColumnName());
    }


    /**
     * Finds the index of the specified column in this schema, or returns -1
     * if the schema contains no column of the specified name.  The
     * column-info object is not required to specify a table name; however, if
     * the table name is unspecified and the column name is ambiguous then an
     * exception will be thrown.
     *
     * @param colInfo column-info object to use for looking up the column in
     *        the schema
     *
     * @return the zero-based index of the column, or -1 if the schema does
     *         not contain a column of the specified name.
     *
     * @throws IllegalArgumentException if {@code colInfo} is {@code null}
     * @throws SchemaNameException if {@code colInfo} doesn't specify a table
     *         name, and multiple columns have the specified column name
     */
    public int getColumnIndex(ColumnInfo colInfo) {
        if (colInfo == null)
            throw new IllegalArgumentException("colInfo cannot be null");

        return getColumnIndex(colInfo.getTableName(), colInfo.getName());
    }


    /**
     * Finds the index of the specified column in this schema, or returns -1
     * if the schema contains no column of the specified name.  The table name
     * is unspecified; if the column name is ambiguous then an exception will
     * be thrown.
     *
     * @param colName the column name to look up
     *
     * @return the zero-based index of the column, or -1 if the schema does
     *         not contain a column of the specified name.
     *
     * @throws IllegalArgumentException if {@code colName} is {@code null}
     * @throws SchemaNameException if multiple columns have the specified
     *         column name
     */
    public int getColumnIndex(String colName) {
        return getColumnIndex(null, colName);
    }


    /**
     * Finds the index of the specified column in this schema, or returns -1
     * if the schema contains no column of the specified name.  The table name
     * may be specified or it may be {@code null}; if {@code null} and the
     * column name is ambiguous then an exception will be thrown.
     *
     * @param tblName the table name, or {@code null} if the table name is not
     *        known or unspecified
     * @param colName the column name to look up
     *
     * @return the zero-based index of the column, or -1 if the schema does
     *         not contain a column of the specified name.
     *
     * @throws IllegalArgumentException if {@code colName} is {@code null}
     * @throws SchemaNameException if {@code tblName} is {@code null} and
     *         multiple columns have the specified column name
     */
    public int getColumnIndex(String tblName, String colName) {
        if (colName == null)
            throw new IllegalArgumentException("colName cannot be null");

        ArrayList<IndexedColumnInfo> colList = colsHashedByColumn.get(colName);

        if (colList == null)
            return -1;

        if (tblName == null) {
            if (colList.size() > 1) {
                throw new SchemaNameException("Column name \"" + colName +
                    "\" is ambiguous in this schema.");
            }

            return colList.get(0).colIndex;
        }
        else {
            // Table-name is specified.

            for (IndexedColumnInfo c : colList) {
                if (tblName.equals(c.colInfo.getTableName()))
                    return c.colIndex;
            }
        }

        return -1;
    }


    /**
     * Given a list of column names, this method returns an array containing
     * the indexes of the specified columns.
     *
     * @param columnNames a list of column names in the schema
     *
     * @return an array containing the indexes of the columns specified in the
     *         input
     *
     * @throws SchemaNameException if a column name is specified multiple
     *         times in the input list, or if a column name doesn't appear in
     *         the schema
     */
    public int[] getColumnIndexes(List<String> columnNames) {
        int[] result = new int[columnNames.size()];
        HashSet<String> s = new HashSet<>();

        int i = 0;
        for (String colName : columnNames) {
            if (!s.add(colName)) {
                throw new SchemaNameException(String.format(
                    "Column %s was specified multiple times", colName));
            }

            result[i] = getColumnIndex(colName);
            if (result[i] == -1) {
                throw new SchemaNameException(String.format(
                    "Schema doesn't contain a column named %s", colName));
            }

            i++;
        }

        return result;
    }


    /**
     * Given a (possibly wildcard) column-name, this method returns the collection
     * of all columns that match the specified column name.  The collection is a
     * mapping from integer indexes (the keys) to <code>ColumnInfo</code> objects
     * from the schema.
     * <p>
     * Any valid column-name object will work, so all of these options are
     * available:
     * <ul>
     *   <li><b>No table, only a column name</b> - to resolve an unqualified
     *     column name, e.g. in an expression or predicate</li>
     *   <li><b>A table and column name</b> - to check whether the schema contains
     *     such a column</li>
     *   <li><b>A wildcard without a table name</b> - to retrieve all columns in
     *     the schema</li>
     *   <li><b>A wildcard with a table name</b> - to retrieve all columns
     *     associated with a particular table name</li>
     * </ul>
     */
    public SortedMap<Integer, ColumnInfo> findColumns(ColumnName colName) {

        TreeMap<Integer, ColumnInfo> found = new TreeMap<>();

        if (colName.isColumnWildcard()) {
            // Some kind of wildcard column-name object.

            if (!colName.isTableSpecified()) {
                // Wildcard with no table name:  *
                // Add all columns in the schema to the result.

                for (int i = 0; i < columnInfos.size(); i++)
                    found.put(i, columnInfos.get(i));
            }
            else {
                // Wildcard with a table name:  tbl.*
                // Find the table info and add its columns to the result.

                HashMap<String, IndexedColumnInfo> tableCols =
                    colsHashedByTable.get(colName.getTableName());

                if (tableCols != null) {
                    for (IndexedColumnInfo indexedColInfo: tableCols.values())
                        found.put(indexedColInfo.colIndex, indexedColInfo.colInfo);
                }
            }
        }
        else {
            // A non-wildcard column-name object.

            if (!colName.isTableSpecified()) {
                // Column name with no table name:  col
                // Look up the list of column-info objects grouped by column name.

                ArrayList<IndexedColumnInfo> colList =
                    colsHashedByColumn.get(colName.getColumnName());

                if (colList != null) {
                    for (IndexedColumnInfo indexedColInfo : colList)
                        found.put(indexedColInfo.colIndex, indexedColInfo.colInfo);
                }
            }
            else {
                // Column name with a table name:  tbl.col
                // Find the table info and see if it has the specified column.

                HashMap<String, IndexedColumnInfo> tableCols =
                    colsHashedByTable.get(colName.getTableName());

                if (tableCols != null) {
                    IndexedColumnInfo indexedColInfo =
                        tableCols.get(colName.getColumnName());
                    if (indexedColInfo != null)
                        found.put(indexedColInfo.colIndex, indexedColInfo.colInfo);
                }
            }
        }

        return found;
    }


    /**
     * Adds a column with given index to list of NOT NULL constrained columns.
     *
     * @param colIndex the integer index of the column to NOT NULL constrain.
     *
     * @return true if the column previous was NULLable, or false if the
     *         column already had a NOT NULL constraint on it before this call.
     */
    public boolean addNotNull(int colIndex) {
        if (colIndex < 0 || colIndex >= numColumns()) {
            throw new IllegalArgumentException("Column index must be between" +
                " 0 and " + numColumns() + "; got " + colIndex + " instead.");
        }
        return notNullCols.add(colIndex);
    }


    /**
     * Removes a column with given index from the list of NOT NULL constrained
     * columns.
     *
     * @param colIndex the integer index of the column to remove the NOT NULL
     *        constraint from.
     */
    public boolean removeNotNull(int colIndex) {
        if (colIndex < 0 || colIndex >= numColumns()) {
            throw new IllegalArgumentException("Column index must be between" +
                " 0 and " + numColumns() + "; got " + colIndex + " instead.");
        }
        return notNullCols.remove(colIndex);
    }


    public boolean isNullable(int colIndex) {
        return !notNullCols.contains(colIndex);
    }


    /**
     * Returns a set of columns that have a NOT NULL constraint, specified by
     * the indexes of the columns in the table schema.
     *
     * @return set of integers - indexes of columns with NOT NULL constraint
     */
    public Set<Integer> getNotNull() {
        return Collections.unmodifiableSet(notNullCols);
    }


    /**
     * Returns the primary key on this table, or {@code null} if there is no
     * primary key.
     *
     * @return the primary key on this table, or {@code null} if there is no
     *         primary key.
     */
    public KeyColumnRefs getPrimaryKey() {
        for (KeyColumnRefs ck : candidateKeys) {
            if (ck.getConstraintType() == TableConstraintType.PRIMARY_KEY)
                return ck;
        }

        return null;
    }


    /**
     * Adds another candidate key to the schema.
     *
     * @param ck the candidate key to add to the schema.
     *
     * @throws IllegalArgumentException if {@code ck} is {@code null}, or if
     *         {@code ck} is a primary key and the schema already contains a
     *         primary key.
     */
    public void addCandidateKey(KeyColumnRefs ck) {
        if (ck == null)
            throw new IllegalArgumentException("ck cannot be null");

        // Make sure we don't have more than one primary key.
        if (ck.getConstraintType() == TableConstraintType.PRIMARY_KEY &&
            getPrimaryKey() != null) {
            throw new TableException("Schema already has a primary key");
        }

        candidateKeys.add(ck);
    }


    /**
     * Returns a count of how many candidate keys are present on the schema.
     *
     * @return a count of how many candidate keys are present on the schema.
     */
    public int numCandidateKeys() {
        return candidateKeys.size();
    }


    /**
     * Returns an unmodifiable list of candidate keys present on the schema.
     *
     * @return an unmodifiable list of candidate keys present on the schema.
     */
    public List<KeyColumnRefs> getCandidateKeys() {
        return Collections.unmodifiableList(candidateKeys);
    }


    /**
     * Returns {@code true} if this schema has a candidate key on the set of
     * columns specified in the argument.  The columns are specified by an
     * array of zero-based indexes.
     *
     * @param colIndexes the set of columns to check against this table
     *        to see if it's a candidate key
     *
     * @return {@code true} if this table has a candidate key on the
     *         specified columns; {@code false} otherwise
     */
    public boolean hasKeyOnColumns(int[] colIndexes) {
        return (getKeyOnColumns(colIndexes) != null);
    }


    /**
     * Returns {@code true} if this schema has a candidate key on the set of
     * columns specified in the argument.  The columns are specified by a
     * {@code ColumnRefs} object.
     *
     * @param colRefs the set of columns to check against this table to see if
     *        it's a candidate key
     *
     * @return {@code true} if this table has a candidate key on the
     *         specified columns; {@code false} otherwise
     */
    public boolean hasKeyOnColumns(ColumnRefs colRefs) {
        return hasKeyOnColumns(colRefs.getCols());
    }


    /**
     * Returns any candidate-key from this schema that has the specified set
     * of columns.  Note that the key's columns may be in a different order
     * than those specified in the argument.
     *
     * @param colIndexes the set of columns to check against this table
     *        to see if it's a candidate key
     *
     * @return a candidate key on the specified columns, or {@code null}
     *         if the schema contains no key on the specified columns
     */
    public KeyColumnRefs getKeyOnColumns(int[] colIndexes) {
        for (KeyColumnRefs ck : candidateKeys)
            if (ck.hasSameColumns(colIndexes))
                return ck;

        return null;
    }


    /**
     * Returns any candidate-key from this schema that has the specified set
     * of columns.  Note that the key's columns may be in a different order
     * than those specified in the argument.
     *
     * @param colRefs the set of columns to check against this table to see if
     *        it's a candidate key
     *
     * @return a candidate key on the specified columns, or {@code null}
     *         if the schema contains no key on the specified columns
     */
    public KeyColumnRefs getKeyOnColumns(ColumnRefs colRefs) {
        return getKeyOnColumns(colRefs.getCols());
    }


    /**
     * Returns all candidate-keys from this schema that have the specified set
     * of columns.  Note that keys may specify columns in a different order
     * than those specified in the argument.  If there are no keys on the
     * specified columns, this method will return an empty list.
     *
     * @param colIndexes the set of columns to check against this table
     *        to see if it's a candidate key
     *
     * @return a list of candidate keys on the specified columns
     */
    public List<KeyColumnRefs> getAllKeysOnColumns(int[] colIndexes) {
        ArrayList<KeyColumnRefs> keys = new ArrayList<>();

        for (KeyColumnRefs ck : candidateKeys) {
            if (ck.hasSameColumns(colIndexes))
                keys.add(ck);
        }

        return keys;
    }


    /**
     * Returns all candidate-keys from this schema that have the specified set
     * of columns.  Note that keys may specify columns in a different order
     * than those specified in the argument.  If there are no keys on the
     * specified columns, this method will return an empty list.
     *
     * @param colRefs the set of columns to check against this table
     *        to see if it's a candidate key
     *
     * @return a list of candidate keys on the specified columns
     */
    public List<KeyColumnRefs> getAllKeysOnColumns(ColumnRefs colRefs) {
        return getAllKeysOnColumns(colRefs.getCols());
    }


    /**
     * Adds the specified table to the set of tables that reference this
     * table.
     *
     * @param referencingTableName the name of the table that references this
     *        table
     * @return {@code true} if the table wasn't previously in this table's set
     *         of referencing tables, or {@code false} if the table was
     *         already in the set of referencing tables
     */
    public boolean addReferencingTable(String referencingTableName) {
        return referencingTables.add(referencingTableName);
    }


    public void removeReferencingTable(String referencingTableName) {
        referencingTables.remove(referencingTableName);
    }


    public void addIndex(IndexColumnRefs index) {
        if (index == null)
            throw new IllegalArgumentException("index cannot be null");

        String indexName = index.getIndexName();

        if (indexes.containsKey(indexName)) {
            throw new TableException("Schema already has an index named " +
                indexName);
        }

        indexes.put(indexName, index);
    }


/*
    public void dropIndex(String idxName) {
        if (idxName == null)
            throw new IllegalArgumentException("drop index must specify an index name");

        if (!indexes.containsKey(idxName))
            throw new IllegalArgumentException("table does not have this index to drop");

        if (primaryKey != null && primaryKey.getIndexName().equals(idxName))
            primaryKey = null;
        Iterator<KeyColumnRefs> it = candidateKeys.iterator();
        while (it.hasNext()) {
            if (it.next().getIndexName().equals(idxName))
                it.remove();
        }
        /* Foreign keys should never be able to be dropped this way * /

        indexes.remove(idxName);
    }
*/

    public void addForeignKey(ForeignKeyColumnRefs fk) {
        foreignKeys.add(fk);
    }


    public int numForeignKeys() {
        return foreignKeys.size();
    }


    public List<ForeignKeyColumnRefs> getForeignKeys() {
        return Collections.unmodifiableList(foreignKeys);
    }


    public Set<String> getReferencingTables() {
        return Collections.unmodifiableSet(referencingTables);
    }


    public Collection<IndexColumnRefs> getIndexes() {
        return Collections.unmodifiableCollection(indexes.values());
    }


    public IndexColumnRefs getIndex(String indexName) {
        return indexes.get(indexName);
    }


    /*
     * Given a set of column names, this method returns the names of all
     * indexes built on these columns.
     *
     * @param columnNames the names of columns to test for
     * @return a set of index names built on the specified columns
     *
    public Set<String> getIndexNames(List<String> columnNames) {
        int[] colIndexes = getColumnIndexes(columnNames);
        ColumnRefs index = new ColumnRefs(colIndexes);

        Set<String> indexNames = new HashSet<>();
        for (Map.Entry<String, ColumnRefs> entry : indexes.entrySet()) {
            if (index.hasSameColumns(entry.getValue()))
                indexNames.add(entry.getKey());
        }

        return indexNames;
    }
*/

    public Set<String> getIndexNames() {
        return new HashSet<>(indexes.keySet());
    }


    @Override
    public String toString() {
        return "Schema[cols=" + columnInfos.toString() + "]";
    }
}