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SQL programmingYou can use the HCL OneDB™ implementation of the SQL language to develop applications for HCL OneDB™ database servers.
Guide to SQL: SyntaxThe HCL OneDB™ Guide to SQL: Syntax describes the syntax of the statements, data types, expressions, operators, and built-in functions of the HCL OneDB™ dialect of the SQL language.
SQL statementsThis chapter describes the syntax and semantics of SQL statements that are recognized by HCL OneDB™.
ALTER TABLE statementUse the ALTER TABLE statement to modify the schema of an existing table.
MODIFY Clause Use the MODIFY clause to change the data type, length, or default value of a column, to add or remove the security label of a column, to allow or disallow NULL values in a column, or to reset the serial counter of a SERIAL, SERIAL8, or BIGSERIAL column.
Adding a Constraint on a Non-Opaque Column

Adding a Constraint on a Non-Opaque Column

ALTER TABLE ... MODIFY operations that use the Single Column Constraint format to implicitly create an index on a non-opaque column also automatically calculate the distribution of the specified column. The distribution statistics are available to the query optimizer when it designs query plans for the table on which the constraint is defined:

For columns on which the new constraint is implemented as a B-tree index, the recalculated column distribution statistics are equivalent to distributions created by the UPDATE STATISTICS statement in HIGH mode.
If the new constraint is not implemented as a B-tree index, the automatically recalculated statistics correspond to distributions created by the UPDATE STATISTICS statement in LOW mode.

See also the section Automatic Calculation of Distribution Statistics in the description of the CREATE INDEX statement for additional information about statistical distributions that are produced automatically when an index or constraint is created on an existing table.

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