某些其他数据库让它们在任何参数为 NULL 时返回 NULL,而不是在所有参数都为 NULL 时才返回 NULL。 1.2 nullif NULLIF(value1, value2) 当value1和value2相等时,NULLIF返回一个空值。 否则它返回value1。 1.3 COALESCE COALESCE(value [, ...]) COALESCE函数返回它的第一个非空参数的值。当且仅当所有参数都...
[null]案例2:selectid,title,coalesce(excerpt,left(body,40))fromposts;结果:由结果得知null值的会做处理,但是对于''是不做处理的 id title excerpt1test post1test post excerpt12test post23test post3test post body3案例3:selectid,title,coalesce(nullif(excerpt,''),left(body,40))fromposts;结果:由...
'index hit rate' AS name, (sum(idx_blks_hit)) / nullif(sum(idx_blks_hit + idx_blks_read),0) AS ratio FROM pg_statio_user_indexes UNION ALL SELECT 'table hit rate' AS name, sum(heap_blks_hit) / nullif(sum(heap_blks_hit) + sum(heap_blks_read),0) AS ratio FROM pg_statio_...
COALESCE –return the first non-null argument. You can use it to substitute NULL by a default value. NULLIF –return NULL if the first argument equals the second one. CAST –convert from one data type into another e.g., from a string into an integer, from a string into a date. Secti...
nvl(expr1,expr2) 当expr1为空时返回expr2,否则返回expr1 nvl2(expr1,expr2,expr3) 当expr1不为空时返回expr2,为空时返回expr3 nullif(expr1,expr2) 若expr1=expr2 那么返回null,否则返回expr1 coalesce(expr1,expr2,…,exprn) nvl的升级版,如果expr1为空返回expr2,如果expr再为空,返回expr3… 1....
PostgreSQL has a function name “COALESCE” [3]. The function takes n number of arguments and returns the first, not null arguments. You can test your expression against NULL using the function. Shell 1 COALESCE (NULL, 2 , 1); NULLIF There is another function called “NULLIF”[3], retur...
NULLIF Takes two argument NULLIF(a,b); if a = b then value is NULL else a SELECT 10/0; ERROR: division by zero SELECT 10/NULLIF(10,5); ?column? 1 (1 row) SELECT 10/NULLIF(5,10); ?column? 2 (1 row) SELECT 10/NULLIF(10,10); ?column? -- (1 row) SELECT COALESCE(10/NUL...
同样,相等运算符适用于文本值。...函数返回参数中第一个非NULL的值,要求参数中至少有一个是非NULL的,如果参数都为NULL则报错: COALESCE (NULL, 2 , 1); 3)NULLIF 另外一个函数是NULLIF,如果两个参数相等 2.2K20 Postgresql中ParamListInfoData的作用 ParamListInfoData是参数的统一抽象,例如 在pl中执行raise ...
COALESCE 238 9.17.3. NULLIF 239 9.17.4. GREATEST and LEAST 239 9.18. 数组函数和操作符 239 9.19. 范围函数和操作符 242 9.20. 聚合函数 244 9.21. 窗口函数 249 9.22. 子查询表达式 250 9.22.1. EXISTS 250 9.22.2. IN 251 9.22.3. NOT IN 251 9.22.4. ANY/ SOME 252 9.22.5. ALL 252 ...
COALESCE –return the first non-null argument. You can use it to substitute NULL by a default value. NULLIF –return NULL if the first argument equals the second one. CAST –convert from one data type into another e.g., from a string into an integer, from a string into a date. Secti...