The difference SQLServer Oracle MySQL
| SqlServser: Microsoft product, can be converted to SQLServer database through ODBC interface Good Access, FoxPro, Excel. |
| Oracle: runs on all major platforms, fully support all industry standards (ODBC, JDBC, OCI), a completely open policy. Oracle Parallel Server by making a set of nodes in the cluster share the same ability to work extended Windows NT to improve the availability and highly scalable cluster solution. Support large concurrent access to a large amount. expensive. |
| MySql: does not support transactions, no view, no stored procedures and triggers, there is no function of the end user to customize the database can not be fully applicable standard SQL syntax. Currently it might have supported. |
| Distinct types | SQLServer | Oracle | MySQL |
| [String concatenation] | + | || | concat() |
| [Control Processing Number] | isnull() | | -NVL NVL (expr1, expr2) if the first argument is null, then the first show the second argument if the first argument is not empty, the first parameter is displayed | -NVL2 NVL2 (expr1, expr2, expr3) if the first argument is null second parameter is displayed, the display is not empty third argument | -NULLIF (expr1, expr2) expr1 and expr2 are equal returns NULL, otherwise it returns the first value |
| -Ifnull (expr1, expr2) if the first argument is null, then the first show the second argument if the first argument is not empty, the first parameter display | -Isnull (expr) represents a parameter to determine whether it is null, null to 1, otherwise 0 | -NULLIF (expr1, expr2) expr1 and expr2 are equal returns NULL, otherwise it returns the first value |
| [System time] | getdate() | sysdate | now() |
| [Date Format] | convert(varchar(8),getdate(),112) | to_char(sysdate,'yyyyMMdd') | data_format(xcs_received_date,'%Ym%d') |
| [检查是否有表再删除] | IF OBJECT_ID('xxx') IS NOT NULL 需要用到系统表(dbo.sysobjects) | select count(1) from user_tables where tablename ='xxx' | drop table if exists tablename |