SQL> select 1-null from dual; SQL> select 1*null from dual; SQL> select 1/null from dual; 查询到一个记录. 注:这个记录就是SQL语句中的那个null 设置某些列为空值 update table1 set 列1=NULL where 列1 is not null; === union 与 union all的区别 UNION ALL selects all rows from each ...
max-wait: 60000 validation-query: SELECT 1 FROM DUAL test-on-borrow: true test-on-return: true test-while-idle: true time-between-eviction-runs-millis: 60000 min-evictable-idle-time-millis: 300000 ds02: username: *** password: *** url: jdbc:oracle:thin:@***:1521/ds02 type: com.a...
1. Oracle 中的 DUAL 表在Oracle中,DUAL表是一个非常常见的内置伪表。...SQLite 中的 DUAL 表 SQLite类似于PostgreSQL,它没有专门的DUAL表。不过,同样可以直接执行不依赖任何表的查询: SELECT 'Hello, SQLite!'...Oracle数据库通常会设置 validation-query 为: SELECT 1 FROM DUAL 这条SQL通过查询DUAL表,返回...
一、Mysql中: INSERT INTO books (name) SELECT 'SongXingzhu' FROM dual WHERE NOT EXISTS (SELECT id FROM books WHERE id = 1) 二、Sqlite中: 由于Sqlite中没有临时表:dual 所以,需要这样写 INSERT INTO books (name) SELECT 'Songxingzhu' WHERE NOT EXISTS (SELECT id FROM books WHERE id = 1) ...
这种操作也是经常用到的,一般Sqlserver是用SELECT SCOPE_IDENTITY() 语句操作,Access用的是SELECT @@IDENTITY,Oracle由于用的是序列,所以是SELECT Seq_TestTable.Currval ID From Dual这样的操作,Sqlite呢,他也有自己的特殊语句了,就是:Select LAST_INSERT_ROWID() ,是不是比较容易记住呢。
这种操作也是经常用到的,一般Sqlserver是用SELECT SCOPE_IDENTITY() 语句操作,Access用的是SELECT @@IDENTITY,Oracle由于用的是序列,所以是SELECT Seq_TestTable.Currval ID From Dual这样的操作,Sqlite呢,他也有自己的特殊语句了,就是:Select LAST_INSERT_ROWID() ,是不是比较容易记住呢。
SELECT * FROM dual WHERE SYSDATE >= DECODE(NVL(1,0),0,NULL,SYSDATE); -- This returns row SELECT * FROM dual WHERE SYSDATE <= DECODE(NVL(1,0),0,NULL,SYSDATE); -- No output if we use <= SELECT * FROM dual WHERE SYSDATE <= DECODE(NVL(1,0),0,SYSDATE,SYSDATE); - 浏览7提...
SELECT DBMS_OBFUSCATION_TOOLKIT.MD5(input_string=>'1') FROM DUAL. Result form showed in Query Editor would be closed after a new query was run. Beautify SQL returned an invalid SQL syntax, e.g. formatted xxx@yyy into xxx @ yyy. "Cannot call Start on a running or suspended thread" ...
WITH TMP AS (SELECT 1 AS ID, 10 AS SAL FROM DUAL UNION SELECT 2 AS ID, 20 AS SAL FROM DUAL UNION SELECT 3 AS ID, 30 AS SAL FROM DUAL UNION SELECT 4 AS ID, 10 AS SAL FROM DUAL)SELECT T.ID, T.SAL, SUM(S.SAL) FROM TMP T, TMP S WHERE ...
不要用 select sysdate into 变量名 from dual; 13、处理业务逻辑时,先锁A表再锁B表,所有的处理都要按照这个顺序,否则会产生死锁。 14、使用for update 语句时应加限制条件,避免不必要的表锁或行锁。 15、少用select 嵌套写法,如select ... from table1 ,(select ... from table2) ... , ...