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通常采用列引用的形式,通过将数据与运算符或函数进行组合构成表达式。
expression: case-expression | constant | [correlation-name.]column-name | - expression | expression operator expression | ( expression ) | function-name ( expression, ... ) | if-expression | special value | input-parameter
case-expression: CASE expression WHEN expression THEN expression,... [ ELSE expression ] END
alternative form of case-expression: CASE WHEN search-condition THEN expression,... [ ELSE expression ] END
constant: integer | number | string | host-variable
special-value: CURRENT { DATE | TIME | TIMESTAMP } | NULL | SQLCODE | SQLSTATE
if-expression: IF condition THEN expression [ ELSE expression ] ENDIF
input-parameter: { ? | :name [ : indicator-name ] }
operator: { + | - | * | / | || | % }
表达式中的常量表达式中的列名称IF 表达式CASE 表达式集合表达式表达式中的子查询输入参数