SQL Case表达式是一种条件表达式,用于在SQL查询中根据不同的条件返回不同的结果。它可以根据给定的条件进行逻辑判断,并根据判断结果返回相应的值或执行相应的操作。 Case表达式通常有两种形式:...
CASE With ELSE ACASEstatement can have an optionalELSEclause. TheELSEclause is executed if none of the conditions in theCASEstatement is matched. Syntax SELECTcustomer_id, first_name,CASEWHENcondition1THENresult1WHENcondition2THENresult2-- Add more WHEN conditions and results as neededELSEelse_resu...
CASEWHENcondition1THENresult1WHENcondition2THENresult2WHENcondition3THENresult3...ELSEdefault_resultEND; 其中,condition1、condition2、condition3等表示需要比较的条件,result1、result2、result3等表示满足对应条件时的操作结果,default_result表示当expression不满足任何条件时的默认结果。 下面通过一个简单的例子来说...
SELECT * FROM tablename [START WITH <condition1>] CONNECT BY <condition2>; 其中START WITH子句用于指定起始条件,即<condition1>,循环关联条件为<condition2>,其中可以使用PRIOR关键字来表示来自于上一循环的列。例如上节中所述的树遍历的例子,使用Oracle的Connect By语法,语句如下: SELECT * FROM tree START...
不过case when并不是专门用来做过滤的,语法使用起来也不叫复杂,也不是所有聚合函数都满足这种过滤的语意。除了case when,还有一种专门的选择性聚合算子,可以对每个聚合函数附加一个过滤条件。具体语法如: SELECT key, AGG1(x) FILTER (WHERE condition1), AGG2(y) FILTER (WHERE condition2), AGG3(z) ...
[WITH [RECURSIVE] with_query [,…] ] SELECT … 其中,with_query的语法为: with_query_name [ ( column_name [, ...] ) ] AS ( {select | values | insert | update | delete} ) 关键要点如下: 每个CTE的AS语句指定的SQL语句,必须是可以返回查询结果的语句,可以是普通的SELECT语句,也可以是INSERT...
简单CASE WHEN函数只能应对一些简单的业务场景,而CASE WHEN条件表达式的写法则更加灵活。 CASE WHEN条件表达式函数:类似JAVA中的IF ELSE语句。 格式: CASEWHENconditionTHENresult[WHEN...THEN...]ELSEresultEND condition是一个返回布尔类型的表达式,如果表达式返回true,则整个函数返回相应result的值,如果表达式皆为false...
The SQL CASE ExpressionThe CASE expression goes through conditions and returns a value when the first condition is met (like an if-then-else statement). So, once a condition is true, it will stop reading and return the result. If no conditions are true, it returns the value in the ELSE...
TheCASEexpression evaluates its conditions sequentially and stops with the first condition whose condition is satisfied. In some situations, an expression is evaluated before aCASEexpression receives the results of the expression as its input. Errors in evaluating these expressions are possible. Aggregate...
SELECT*FROMtablename [STARTWITH<condition1>]CONNECTBY<condition2>;其中START WITH子句用于指定起始条件...