NULL字段参与运算或判断结果均为NULL 用IFNULL(value1,value2),将value1为NULL的值替换成value2;(1) 比较运算符: 字符串和其他类型比较存在隐式转换为比较类型,如果转换不成功则默认为0; 用<=>来将NULL作为一般数值来判断。(2) ISNULL和ISNOTNULL(3) 上述(1)(2)(3)三种方法为正确处理NULL数据的方法。
,可以看到,此时为无主键表。 obclient [SYS]> select dbms_metadataget_ddl('TABLE','IB_WL_BILLTABLOG','XXIB') STR from dual\G *** 1. row *** STR: CREATE TABLE "IB_WL_BILLTABLOG ( "LOGID" NUMBER(14) CONSTRAINT "IB_WL_BILLTABLOG_OBNOTNULL_1688521203675300" NOT NULL ENABLE, ...
所谓的外键约束就是引用字段必须在被引用字段中存在,除非引用字段部分为NULL或全部为NULL(由MATCH TYPE决定),否则INSERT或UPDATE时将返回失败,且被引用字段必须有唯一约束或是主键。 外键约束语法相对较复杂一点,创建外键的语法如下: ALTER TABLE tbl_foreign CONSTRAINT fk_constraint FOREIGN KEY(col1,col2) REFERENCES...
27、 数据库有一个原则是代码离数据越近越好,所以优先选择Default,依次为Rules,Triggers, Constraint(约束如外健主健CheckUNIQUE……,数据类型的最大长度等等都是约束),Procedure.这样不仅维护工作小,编写程 序质量高,并且执行的速度快。 28、如果要插入大的二进制值到Image列,使用存储过程,千万不要用内嵌INsert来...
MySQL 是不支持 select ... into ，但是可以使用 insert into ... select 当然也可以使用 create...
NOT NULLis there, because it tries to match it too early before any downcasts are tried.
Adding NOT NULL DEFAULT VALUE column to existing table with data Adding of counter column Adding varchar(8) in time format that totals more than 24 hrs in SQL Additional Column With BULK INSERT Adventureworks query about sales AFTER INSERT and AFTER UPDATE triggers on same table After INSERT Tr...
not any sort of relational theory. If you instead replace this NULL with a value subtracted from the types available range of values (by a NOT NULL column, a COALESCE in a left join, or in your case the UNION), this in my understanding of what you're saying is a "token" saying the...
used in a table definition: "ERROR 1171: All parts of a PRIMARY KEY must be NOT NULL; If you need NULL in a key, use UNIQUE instead" but "ISO/IEC 9075-1:1999 (E)" says in "4.6.6.3 Table constraints": "A primary key constraint is a unique constraint that specifies PRIMARY KEY....
DTS_E_EXEC2000PKGTASK_ERROR_IN_VALIDATE 欄位 DTS_E_EXEC2000PKGTASK_FILE_NAME_NOT_SPECIFIED 欄位 DTS_E_EXEC2000PKGTASK_HANDLER_NOT_FOUND 欄位 DTS_E_EXEC2000PKGTASK_INITIALIZATION_WITH_WRONG_XML_ELEMENT 欄位 DTS_E_EXEC2000PKGTASK_NOT_PRIMITIVE_TYPE 欄位 DTS_E_EXEC2000PKGTASK_NULL_VALUE ...