ddl

Add ON DELETE CASCADE behavior to an sqlite3 table after it has been created

由 让人想犯罪 __ 提交于 2019-12-17 05:14:38
问题 Is it possible to add an ON DELETE CASCADE to a table after it has been created? My schema is as follows: CREATE TABLE skills(name varchar, skill varchar, level int, foreign key(name) references runners(name), primary key(name, skill)); And I would like to cascade if the foreign key is deleted. 回答1: SQLite's ALTER TABLE command cannot do what you want. However, it is possible to bypass the SQL interpreter and change the internal table definition directly. SQLite stores table definitions as a

Add ON DELETE CASCADE behavior to an sqlite3 table after it has been created

由 爷，独闯天下 提交于 2019-12-17 05:14:27
问题 Is it possible to add an ON DELETE CASCADE to a table after it has been created? My schema is as follows: CREATE TABLE skills(name varchar, skill varchar, level int, foreign key(name) references runners(name), primary key(name, skill)); And I would like to cascade if the foreign key is deleted. 回答1: SQLite's ALTER TABLE command cannot do what you want. However, it is possible to bypass the SQL interpreter and change the internal table definition directly. SQLite stores table definitions as a

深入理解MDL元数据锁

由 爷，独闯天下 提交于 2019-12-16 09:54:12
前言： 当你在MySQL中执行一条SQL时，语句并没有在你预期的时间内执行完成，这时候我们通常会登陆到MySQL数据库上查看是不是出了什么问题，通常会使用的一个命令就是 show processlist，看看有哪些session，这些session在做什么事情。当你看到 waiting for table metadata lock 时，那就是遇到MDL元数据锁了。本篇文章将会介绍MDL锁的产生与排查过程。 1.什么是MDL锁 MDL全称为metadata lock，即元数据锁。MDL锁主要作用是维护表元数据的数据一致性，在表上有活动事务（显式或隐式）的时候，不可以对元数据进行写入操作。因此从MySQL5.5版本开始引入了MDL锁，来保护表的元数据信息，用于解决或者保证DDL操作与DML操作之间的一致性。 对于引入MDL，其主要解决了2个问题，一个是事务隔离问题，比如在可重复隔离级别下，会话A在2次查询期间，会话B对表结构做了修改，两次查询结果就会不一致，无法满足可重复读的要求；另外一个是数据复制的问题，比如会话A执行了多条更新语句期间，另外一个会话B做了表结构变更并且先提交，就会导致slave在重做时，先重做alter，再重做update时就会出现复制错误的现象。 元数据锁是server层的锁，表级锁，每执行一条DML、DDL语句时都会申请MDL锁，DML操作需要MDL读锁

change column datatype from array to integer

由 我的梦境 提交于 2019-12-14 04:13:11
问题 I need to change the data type of a column from _float8 to int4 ALTER TABLE "table" ALTER COLUMN "col" SET DATA TYPE int4; results in column "col" cannot be cast automatically to type integer ALTER TABLE "table" ALTER COLUMN "col" SET DATA TYPE int4 USING (col::integer); results in cannot cast type double precision[] to integer any ideas? 回答1: You have to point out which element of the array should be used in the conversion, e.g. alter table x alter column y set data type int4 using (y[1]:

Dynamically constructing MySQL Code for creating a trigger

由 浪尽此生 提交于 2019-12-13 19:17:55
问题 I am trying to implement audit trail/logging for a MySQL database. Now I have created an "audit" db (let's call it company_audit ) which will contain "audit" copies of certain tables in the main db. (Say for company.customers I will create company_audit.customers . The audit table will contain the same exact columns as in the original table. I want to use a trigger to insert changes in the original table into the audit table like so: DELIMITER $$ DROP TRIGGER IF EXISTS customers_history_AU$$

SQL Server Conditional Foreign Key Constraints

由 蹲街弑〆低调 提交于 2019-12-13 13:07:47
问题 I'm having trouble figuring out how to create a foreign key constraint. My data model is fixed and out of my control, it looks like this: CREATE TABLE Enquiry (Enquiry_Ref INTEGER PRIMARY KEY CLUSTERED, Join_Ref INTEGER, EnquiryDate, EnquiryType...) CREATE TABLE Contact (Contact_Ref INTEGER PRIMARY KEY CLUSTERED, Surname, Forenames ....) CREATE TABLE UniversalJoin (Join_Ref INTEGER, Contact_Ref INTEGER, Rel_Type INTEGER) Each Enquiry has exactly one Contact. The link between the two is the

Is there any ISO standard of how to write SQL queries in DDL?

由 主宰稳场 提交于 2019-12-13 08:13:42
问题 I am doing my first database project. I would like to know which of the following ways should I use to make SQL queries in DDL. #1 CREATE TABLE employees ( id INTEGER PRIMARY KEY, first_name CHAR(50) NULL, last_name CHAR(75) NOT NULL, dateofbirth DATE NULL ); #2 CREATE TABLE employees ( id INTEGER PRIMARY KEY, first_name CHAR(50) NULL, last_name CHAR(75) NOT NULL, dateofbirth DATE NULL ); #3 CREATE TABLE employees ( ID integer PRIMARY KEY, FIRST_NAME char(50) NULL, LAST_NAME char(75) NOT NULL

HSQLDB UNIQUE constraint and SQL Array Type

由 流过昼夜 提交于 2019-12-13 06:27:17
问题 I am developing with HSQLDB 2.2.9. HSQLDB is one of the RDBMS's out there that supports the SQL Array type and I want to use this capability to address some functionality in my database. I've been running some command line queries as I develop my database, but I am not sure how the UNIQUE constraint is handled by HSQLDB when declared for a column of type VARCHAR(24) ARRAY[]. The DDL I am using follows: CREATE CACHED TABLE Clients ( cli_id INTEGER GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,

Zend framerwork DB DDL update

由 人走茶凉 提交于 2019-12-13 04:02:01
问题 I am new to zend and i want to use the DB module for an application. I have this code $DB = new Zend\Db\Adapter\Adapter(array( 'driver' => 'Mysqli', 'database' => 'database', 'username' => 'user', 'password' => 'pass' )); use Zend\Db\Sql\Ddl; use Zend\Db\Sql\Ddl\Column; use Zend\Db\Sql\Ddl\Constraint; $table = new Ddl\CreateTable('table'); $table->setTable('table'); $table->addColumn(new Column\Integer('id',false,NULL,array('autoincrement'=>true))); $table->addColumn(new Column\Varchar('name'

Postgres 8.3 Query full function definition using a query

由 拥有回忆 提交于 2019-12-13 03:57:15
问题 Is it possible to be able to retrieve the full function definition (with parameters etc) using a SQL query? 回答1: This function or view (doing similar things) works with Postgres 8.3. CREATE AGGREGATE public.textcat_all( basetype = text, sfunc = textcat, stype = text, initcond = '' ); CREATE OR REPLACE FUNCTION public.getfunctionddl(functionOid oid) RETURNS text AS $BODY$ DECLARE funcschema text; funcname text = NULL; paranames text; paramodes text; paratypes text; paraintypes text; function
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