if not exists

Demand:Add a field to a table in a database (if the field already exists, do not do so; if the field does not exist, the new one)Baidu has been n long, did not meet the requirements of the example, only the reference to add their own pondering,

Typically, as a deployment script for an application, the first task that begins is to create a dedicated (dedicated) user and user group for the current app. This script is very simple, a reference sample is attached here:[Plain]View Plaincopy

Here is the MHA from boot, to failover's complete manager.log, and all of the MySQL General.log in the cluster. We can learn more about the workings of MHA through these logs. There is a lot of help in using good MHA.The architecture is as

Title:Database1. Table Name: g_cardapplyField (field name/type/length):G_applyno varchar 8;//application number (keywords)G_applydate bigint 8;//Application DateG_state varchar 2;//Application Status2. Table Name: G_cardapplydetailField (field

The/data/data/package name/databases is the directory where the program holds the data, which is the path returned by the Environment.getdatadirectory () method. After you locate the database, you can select User.db to perform the export.With the

Query is the core of the database, the following for you to introduce MySQL multiple table query How to achieve, if you are in the MySQL multiple table query has encountered problems, may wish to see. mysql multiple table query: Copy Code

String drop table if exists category; CREATE table if not EXISTS category ( C_ID bigint NOT NULL, C_name varchar (255) Default ', C_type int default 1, Primary KEY (C_ID) ); drop table if exists files; CREATE table if not EXISTS files ( f_id bigint

MySQL Create and delete tablesCreate a tableThe Simple WayCREATE TABLE Person (number INT (one), name VARCHAR (255), birthday DATE);or aCREATE TABLE IF not EXISTS person (number INTone), name VARCHAR (255), birthday DATE);To view the MySQL creation

Creation and deletion of databasesI. Database-related commandsCreation of a databaseCreate {Database|schema} db_name [character set=] [collate =]; If the database is present, an error will beCreate {Database|schema} [if not exists] db_name

Below we describe how to implement Mynotes database creation through the API provided by SQLite3. Creating a database typically takes the following three steps.(1) Use the Sqlite3_open function to open the database.(2) Create a database table using

Below we describe how to implement Mynotes database creation through the API provided by SQLite3. Creating a database typically takes the following three steps.(1) Use the Sqlite3_open function to open the database.(2) Create a database table using

Library Management1. Create a databasemysql> help CREATE database; CREATE {DATABASE | SCHEMA} [IF not EXISTS] db_name [create_specification] ... create_specification: [DEFAULT] CHARACTER SET [=] charset_ name | [DEFAULT] COLLATE [=] Collation_name650

" SQL Chapter" "SQL Statement grooming:--based on MySQL5.6" "has been combed: CREATE TABLE" "will persist in perfection"SQL:1. Data Definition Statements:1.3 CREATE TABLE format: 3 Types of Build table statements1. Simple SQL indicates the structure:

1. Create a tableReference: Create-tableCREATE [Temporary] TABLE [IF not EXISTS]tbl_name (field name data type[Not NULL | NULL] [DEFAULT default_value] [auto_increment] [UNIQUE [KEY] | [PRIMARY] KEY][COMMENT ' string '][REFERENCES tbl_name

This is the note I re-wrote after I read the IMOOC video tutorial.Although I've learned about SQL Server databases before, I've also forgotten about them. Now pick it up again, install a database exercise, and use MySQL.The first lesson is the

First, let's talk about why the tables are divided.When a piece of data reaches millions of, you spend more time searching for it, and if you have a joint query, I think it's possible to die there. The purpose of the sub-table is to reduce the

1. Database operationsTo Create a database :CREATE {database| SCHEMA} [IF not EXISTS] Db_nameIf CREATE DATABASE t1[If not EXISTS]: If the library already exists, it will not return an errorDisplay the database encoding method :SHOW CREATE DATABASE T1

Database Operations View all Databases hive> show databases; using the database default hive> Use default; View database Information Hive > describe database default;OkDb_name Comment location owner_name owner_type parametersDefault default Hive

View DatabaseSHOW DATABASES;Create a databaseCREATE database IF not EXISTS name;Select DatabaseUse database name;View data tables in a databaseSHOW TABLES;Deleting a databaseDROP database name IF EXISTS;Create a simple database tableCREATE table IF

Database Storage EngineTo set the default storage engine:vim /etc/my.conf[mysqld]default_storage_engine= InnoDB;To view the storage engines supported by MySQL:show engines;To view the current default storage engine:show variables like