Here are 4 examples illustrating when you would use IF EXISTS and when you would use IF NOT ...
Here are 4 examples illustrating when you would use IF EXISTS and when you would use IF NOT ...
NOT IN 和 <>ALL 对 NULL 值敏感,这意味着 NOT IN 后面的子查询或者常量集合一旦有 NULL 值出现,则整个 SQL 的执行结果就会为 NULL。 所以一旦相关的连接列上出现了 NULL 值(实际只会判断字段是否有 NOT NULL 约束),此时 Oracle 如果还按照通常的 ANTI JOIN 的处理逻辑来处理(实际和 INNER JOIN 的处理逻...
SQL performance on LEFT OUTER JOIN vs NOT EXISTS Joe's link is a good starting point.Quassnoi covers this too. In general,if your fields are properly indexed, OR if you expect to filter out more records (i.e. have a lots of rowsEXISTin the subquery)NOT EXISTSwill perform better. EXIS...
MySQL官方对CREATE TABLE IF NOT EXISTS SELECT给出的解释是: CREATE TABLE IF NOT EXIST… SELECT的行为,先判断表是否存在, 如果存在,语句就相当于执行insert into select; 如果不存在,则相当于create table … select。 当数据表存在的时候,使用insert into select将select的结果插入到数据表中,当select的结果集...
The last exampleisadouble-nestedNOTEXISTSquery. Thatis, it has aNOTEXISTSclause within aNOTEXISTSclause. Formally, it answers the question “does a city existwitha store thatisnotinStores”? But itiseasiertosay that a nestedNOTEXISTSanswers the question “isx TRUEforally?” ...
(SQL does not return the result set, true) As follows: Table A ID NAME 1 A1 2 A2 3 A3 Table B ID AID NAME 11 B1 22 B2 32 B3 Table A and B is 1 to many relationship A.ID = B.AID SELECT, ID, NAME, FROM, A, WHERE, EXIST (SELECT * FROM, B, WHERE, A.ID=B.AID) ...
This issue is caused by the case of the ID.During the execution of a DWS SQL script, the system uses lowercase letters by default. If a field is in upper case, add "".Exa
The following example restricts results toSalesOrderNumberto values starting withSO6andProductKeysgreater than or equal to 400. SQL -- Uses AdventureWorksSELECTProductKey, CustomerKey, OrderDateKey, ShipDateKeyFROMFactInternetSalesWHERESalesOrderNumberLIKE'SO6%'ANDNOTProductKey <400; ...
The remote server "(null)" does not exist. For example, this issue occurs in the following scenario: You publish a table in a transactional publication, and then you set the @allow_drop property to True. You...