Control Structures of PL/SQL Control structures are probably the most useful (and important) part of PL/pgSQL.With PL/pgSQL's control structures, you can manipulate PostgreSQL data in a very flexible and powerful way. 1.Returning From a Function RETU…

Errors and Messages 1. Reporting Errors and Messages Use the RAISE statement to report messages and raise errors. RAISE [ level ] 'format' [, expression [, ... ]] [ USING option = expression [, ... ] ]; RAISE [ level ] condition_name [ USING option =…

1 PL/pgSQL Under the Hood This part discusses some implementation details that are frequently important for PL/pgSQL users to know. 1.1 Variable Substitution SQL statements and expressions within a PL/pgSQL function can refer to variables and paramet…

Trigger Procedures PL/pgSQL can be used to define trigger procedures on data changes or database events. A trigger procedure is created with the CREATE FUNCTION command, declaring it as a function with no arguments and a return type of trigger (for d…

Cursors Rather than executing a whole query at once, it is possible to set up a cursor that encapsulates the query, and then read the query result a few rows at a time. A more interesting usage is to return a reference to a cursor that a function has…

1.Structure of PL/pgSQL The structure of PL/pgSQL is like below: [ <<label>> ] [ DECLARE declarations ] BEGIN statements END [ label ]; A label is only needed if you want to identify the block for use in an EXIT statement, or to qualify the na…

程序控制 程序结构有分支结构与循环结构: 分支结构语法:IF.CASE: 循环结构:FOR.WHILE LOOP:先执行再判断,至少执行一次: WHILE LOOP:先判断再执行,如果不满足条件,就不执行 FOR循环:已知要循环的次数. 如果明确知道循环次数,使用FOR循环: 如果不知道循环次数,但是知道循环结束条件,使用LOOP循环. 循环控制:EXIT与CONTINUE语句完成. PL/SQL程序与其他编程语言一样,也拥有自己的三种程序结构:顺序结构.分支结构.循环结构.这三种不同的结构都有…

1._rowid 类似Oracle的rowid mysql> ; +-------+----+----------------+-------------+---------------+------------+ | rowid | ID | Name | CountryCode | District | Population | +-------+----+----------------+-------------+---------------+------------+ | | | K…

1.MySQL的历史,一些相关概念. 2.MySQL数据类型 *通常一个页内可以存放尽可能多的行,那么数据库的性能就越好,选择一个正确的数据类型至关重要. 1>UNSIGNED类型: 将数字类型无符号化. 2>ZEROFILL: 可以格式化整形显示,一旦启用该属性,MySQL数据库为列自动添加UNSIGNED属性.0填充. 3>日期和时间类型 日期数据类型占用空间的情况 类型 起始范围 结束范围 DATETIME 1000-01-01 00:00:00 9999-12-31 23:59:…

前置知识:awk 参考学习博客:https://www.cnblogs.com/bugingcode/p/8287914.html awk 'BEGIN{ commands } pattern{ commands } END{ commands }' 第一步:运行BEGIN{ commands }语句块中的语句. 第二步:从文件或标准输入(stdin)读取一行.然后运行pattern{ commands }语句块,它逐行扫描文件,从第一行到最后一行反复这个过程.直到文件所有被读取完成. 第三步:…