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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™.
CREATE TABLE statementUse the CREATE TABLE statement to create a new permanent table in the current database.
Column definitionUse the column definition segment of the CREATE TABLE statement to declare the name and data type (and optionally the default value and the constraints or the security label) of a single column of the new table.
Single-Column Constraint FormatUse the Single-Column Constraint format to define and declare the name of at least one constraint on a single column, and to specify the mode of each constraint.
Differences Between a Unique Constraint and a Unique Index

Differences Between a Unique Constraint and a Unique Index

Although a unique index and a unique constraint are functionally similar, besides various differences in the syntax by which you declare, alter, or destroy them, there are additional differences between these two types of database objects:

In DDL statements, they are registered or dropped in different tables of the system catalog
In DML statements, enabled unique constraints on a logged table are checked at the end of a statement, but unique indexes are checked on a row-by-row basis, thereby preventing any insert or update of a row that might potentially violate the uniqueness of the specified column (or for a multiple-column column constraint or index, the column list).

For example, if you stored the values 1, 2, and 3 in rows of a logged table that has an INT column, an UPDATE operation on that table that specifies SET c = c + 1 would fail with an error if there were a unique index on the column c, but the statement would succeed if the column had a unique constraint.

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