Package org.h2.expression

Class Expression

java.lang.Object
org.h2.expression.Expression
All Implemented Interfaces:
HasSQL, Typed
Direct Known Subclasses:
Alias, ArrayConstructorByQuery, BetweenPredicate, CompareLike, Comparison, ConditionAndOr, ConditionAndOrN, ConditionInArray, ConditionInConstantSet, ConditionInList, ConditionInQuery, ConditionLocalAndGlobal, ConditionNot, DataAnalysisOperation, ExistsPredicate, ExpressionColumn, ExpressionList, Function0_1, IsJsonPredicate, JavaFunction, Operation0, Operation1, Operation1_2, Operation2, OperationN, SimpleCase, SimplePredicate, Subquery, UniquePredicate, Wildcard
public abstract class Expression extends Object implements HasSQL, Typed
An expression is a operation, a value, or a function in a query.

  • Field Details

  • Constructor Details

    • Expression

      public Expression()

  • Method Details

    • writeExpressions

      public static StringBuilder writeExpressions(StringBuilder builder, List<? extends Expression> expressions, int sqlFlags)
      Get the SQL snippet for a list of expressions.
      Parameters:
      builder - the builder to append the SQL to
      expressions - the list of expressions
      sqlFlags - formatting flags
      Returns:
      the specified string builder

    • writeExpressions

      public static StringBuilder writeExpressions(StringBuilder builder, Expression[] expressions, int sqlFlags)
      Get the SQL snippet for an array of expressions.
      Parameters:
      builder - the builder to append the SQL to
      expressions - the list of expressions
      sqlFlags - formatting flags
      Returns:
      the specified string builder

    • getValue

      public abstract Value getValue(SessionLocal session)
      Return the resulting value for the current row.
      Parameters:
      session - the session
      Returns:
      the result

    • getType

      public abstract TypeInfo getType()
      Returns the data type. The data type may be unknown before the optimization phase.
      Specified by:
      getType in interface Typed
      Returns:
      the data type

    • mapColumns

      public abstract void mapColumns(ColumnResolver resolver, int level, int state)
      Map the columns of the resolver to expression columns.
      Parameters:
      resolver - the column resolver
      level - the subquery nesting level
      state - current state for nesting checks, initial value is MAP_INITIAL

    • optimize

      public abstract Expression optimize(SessionLocal session)
      Try to optimize the expression.
      Parameters:
      session - the session
      Returns:
      the optimized expression

    • optimizeCondition

      public final Expression optimizeCondition(SessionLocal session)
      Try to optimize or remove the condition.
      Parameters:
      session - the session
      Returns:
      the optimized condition, or null

    • setEvaluatable

      public abstract void setEvaluatable(TableFilter tableFilter, boolean value)
      Tell the expression columns whether the table filter can return values now. This is used when optimizing the query.
      Parameters:
      tableFilter - the table filter
      value - true if the table filter can return value

    • getSQL

      public final String getSQL(int sqlFlags)
      Description copied from interface: HasSQL
      Get the SQL statement of this expression. This may not always be the original SQL statement, specially after optimization.
      Specified by:
      getSQL in interface HasSQL
      Parameters:
      sqlFlags - formatting flags
      Returns:
      the SQL statement

    • getSQL

      public final StringBuilder getSQL(StringBuilder builder, int sqlFlags)
      Description copied from interface: HasSQL
      Appends the SQL statement of this object to the specified builder.
      Specified by:
      getSQL in interface HasSQL
      Parameters:
      builder - string builder
      sqlFlags - formatting flags
      Returns:
      the specified string builder

    • getSQL

      public final String getSQL(int sqlFlags, int parentheses)
      Get the SQL statement of this expression. This may not always be the original SQL statement, especially after optimization.
      Parameters:
      sqlFlags - formatting flags
      parentheses - parentheses mode
      Returns:
      the SQL statement

    • getSQL

      public final StringBuilder getSQL(StringBuilder builder, int sqlFlags, int parentheses)
      Get the SQL statement of this expression. This may not always be the original SQL statement, especially after optimization.
      Parameters:
      builder - string builder
      sqlFlags - formatting flags
      parentheses - parentheses mode
      Returns:
      the specified string builder

    • needParentheses

      public boolean needParentheses()
      Returns whether this expressions needs to be wrapped in parentheses when it is used as an argument of other expressions.
      Returns:
      true if it is

    • getEnclosedSQL

      public final StringBuilder getEnclosedSQL(StringBuilder builder, int sqlFlags)
      Get the SQL statement of this expression. This may not always be the original SQL statement, especially after optimization. Enclosing '(' and ')' are always appended.
      Parameters:
      builder - string builder
      sqlFlags - formatting flags
      Returns:
      the specified string builder

    • getUnenclosedSQL

      public abstract StringBuilder getUnenclosedSQL(StringBuilder builder, int sqlFlags)
      Get the SQL statement of this expression. This may not always be the original SQL statement, especially after optimization. Enclosing '(' and ')' are never appended.
      Parameters:
      builder - string builder
      sqlFlags - formatting flags
      Returns:
      the specified string builder

    • updateAggregate

      public abstract void updateAggregate(SessionLocal session, int stage)
      Update an aggregate value. This method is called at statement execution time. It is usually called once for each row, but if the expression is used multiple times (for example in the column list, and as part of the HAVING expression) it is called multiple times - the row counter needs to be used to make sure the internal state is only updated once.
      Parameters:
      session - the session
      stage - select stage

    • isEverything

      public abstract boolean isEverything(ExpressionVisitor visitor)
      Check if this expression and all sub-expressions can fulfill a criteria. If any part returns false, the result is false.
      Parameters:
      visitor - the visitor
      Returns:
      if the criteria can be fulfilled

    • getCost

      public abstract int getCost()
      Estimate the cost to process the expression. Used when optimizing the query, to calculate the query plan with the lowest estimated cost.
      Returns:
      the estimated cost

    • getNotIfPossible

      public Expression getNotIfPossible(SessionLocal session)
      If it is possible, return the negated expression. This is used to optimize NOT expressions: NOT ID>10 can be converted to ID<=10. Returns null if negating is not possible.
      Parameters:
      session - the session
      Returns:
      the negated expression, or null

    • getTypeIfStaticallyKnown

      public TypeInfo getTypeIfStaticallyKnown(SessionLocal session)
      Returns data type of this expression if it is statically known.
      Parameters:
      session - the session
      Returns:
      data type or null

    • isConstant

      public boolean isConstant()
      Check if this expression will always return the same value.
      Returns:
      if the expression is constant

    • isNullConstant

      public boolean isNullConstant()
      Check if this expression will always return the NULL value.
      Returns:
      if the expression is constant NULL value

    • isValueSet

      public boolean isValueSet()
      Is the value of a parameter set.
      Returns:
      true if set

    • isIdentity

      public boolean isIdentity()
      Check if this is an identity column.
      Returns:
      true if it is an identity column

    • getBooleanValue

      public boolean getBooleanValue(SessionLocal session)
      Get the value in form of a boolean expression. Returns true or false. In this database, everything can be a condition.
      Parameters:
      session - the session
      Returns:
      the result

    • createIndexConditions

      public void createIndexConditions(SessionLocal session, TableFilter filter)
      Create index conditions if possible and attach them to the table filter.
      Parameters:
      session - the session
      filter - the table filter

    • getColumnName

      public String getColumnName(SessionLocal session, int columnIndex)
      Get the column name or alias name of this expression.
      Parameters:
      session - the session
      columnIndex - 0-based column index
      Returns:
      the column name

    • getSchemaName

      public String getSchemaName()
      Get the schema name, or null
      Returns:
      the schema name

    • getTableName

      public String getTableName()
      Get the table name, or null
      Returns:
      the table name

    • getNullable

      public int getNullable()
      Check whether this expression is a column and can store NULL.
      Returns:
      whether NULL is allowed

    • getTableAlias

      public String getTableAlias()
      Get the table alias name or null if this expression does not represent a column.
      Returns:
      the table alias name

    • getAlias

      public String getAlias(SessionLocal session, int columnIndex)
      Get the alias name of a column or SQL expression if it is not an aliased expression.
      Parameters:
      session - the session
      columnIndex - 0-based column index
      Returns:
      the alias name

    • getColumnNameForView

      public String getColumnNameForView(SessionLocal session, int columnIndex, boolean cte)
      Get the column name of this expression for a view.
      Parameters:
      session - the session
      columnIndex - 0-based column index
      cte - true for CTE, false for tables and views
      Returns:
      the column name for a view

    • getNonAliasExpression

      public Expression getNonAliasExpression()
      Returns the main expression, skipping aliases.
      Returns:
      the expression

    • addFilterConditions

      public void addFilterConditions(TableFilter filter)
      Add conditions to a table filter if they can be evaluated.
      Parameters:
      filter - the table filter

    • toString

      public String toString()
      Convert this expression to a String.
      Overrides:
      toString in class Object
      Returns:
      the string representation

    • getSubexpressionCount

      public int getSubexpressionCount()
      Returns count of subexpressions.
      Returns:
      count of subexpressions

    • getSubexpression

      public Expression getSubexpression(int index)
      Returns subexpression with specified index.
      Parameters:
      index - 0-based index
      Returns:
      subexpression with specified index, may be null
      Throws:
      IndexOutOfBoundsException - if specified index is not valid

    • getWhenValue

      public boolean getWhenValue(SessionLocal session, Value left)
      Return the resulting value of when operand for the current row.
      Parameters:
      session - the session
      left - value on the left side
      Returns:
      the result

    • getWhenSQL

      public StringBuilder getWhenSQL(StringBuilder builder, int sqlFlags)
      Appends the SQL statement of this when operand to the specified builder.
      Parameters:
      builder - string builder
      sqlFlags - formatting flags
      Returns:
      the specified string builder

    • isWhenConditionOperand

      public boolean isWhenConditionOperand()
      Returns whether this expression is a right side of condition in a when operand.
      Returns:
      true if it is, false otherwise