文档介绍:mysql中cast的使用方法数据库中cast的使用方法
数据库中cast的使用方法
数据库中cast的使用方法 数据库中cast的使用方法的使用方法你知道吗?下面xx就跟你们具体介绍下 数据库中cast的使用方法的使用方法,期望对你们有用。
数据库中cast的使用方法的使用方法以下:
常常在前辈们的SQL中能够看到CAST的使用方法,比如 WITH T AS(SELECT LEVEL||" " L FROM DUAL CONNECT BY LEVEL=5), A(A,V) AS(SELECT CAST(L AS VARCHAR(30)),1 FROM T UNION ALL SELECT A||L,V+1 FROM A, T WHERE INSTR(A,L)=0 AND V5 ) SELECT * FROM A;
比如上面的with递归语句,不过CAST因为用的比较少,今天就先给 自己扫个盲了,引用Oracle的官方文档中对于CAST的描述以下:
CAST CAST converts values from one data type to another. Return Value The data type specified by type_name. Syntax CAST(expr AS type_name) Arguments expr can be an expression in one of the data types. type_name is one of the data types listed in Table1-2,"Dimensional Data Types". Table 3-1 shows which data types can be cast into which other built-in data types. NUMBER includes NUMBER, DECIMAL, and INTEGER. DATETIMEincludes DATE,TIMESTAMP, TIMESTAMP WITH TIMEZONE, and TIMESTAMP WITH LOCAL TIMEZONE. INTERVAL includes INTERVAL DAY TO SECOND and INTERVAL YEAR TO MONTH. Table 3-1 Compatible Data Types From To BINARY_FLOAT, BINARY_DOUBLE To CHAR, VARCHAR2 To NUMBER To DA