TT_HASH

The TT_HASH function returns the hash value of an expression or list of expressions. This value is the value that is used by a hash index.

SQL syntax

TT_HASH(Expression [,...])

Parameters

TT_HASH has the parameter:

Parameter Description

Expression [,...]

One or more expressions to be used to determine the hash value of the expression or list of expressions.

Description

  • Each expression must have a known data type and must be non-nullable. The hash value of the expression depends on both the value of the expression and its type. For example, TT_HASH of an TT_INTEGER with value 25 may be different from TT_HASH of a NUMBER or BINARY_DOUBLE with value 25. If you specify a list of expressions, the TT_HASH result depends on the order of the expressions in the list.

  • Since constants and expressions that are not simple column references are subject to internal typing rules, over which applications have no control, the best way to ensure that TT_HASH computes the desired value for expressions that are not simple column references is to CAST the expression to the desired type.

  • The result type of TT_HASH is TT_INTEGER in 32-bit mode and TT_BIGINT in 64-bit mode.

  • TT_HASH can be used in a SQL statement anywhere an expression can be used. For example, TT_HASH can be used in a SELECT list, a WHERE or HAVING clause, an ORDER BY clause, or a GROUP BY clause.

  • The output of error messages, trace messages, and ttXactAdmin display the hash value as a signed decimal so that the value matches TT_HASH output.

Examples

The following query finds the set of rows whose primary key columns hash to a given hash value: 

SELECT * FROM t1 
  WHERE TT_HASH(pkey_col1, pkey_col2, pkey_col3) = 12345678;