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Simulate CREATE DATABASE IF NOT EXISTS for PostgreSQL?
I want to create a database which does not exist through JDBC. Unlike MySQL, PostgreSQL does not support create if not exists syntax. What is the best way to accomplish this?
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创建自定义 TinyWebDB 服务 · App Inventor 2 中文网
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Select something that has more/less than x character
... it's possible to select something that has more/less than x characters in SQL.
4 Answers
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Return 0 if field is null in MySQL
In MySQL, is there a way to set the "total" fields to zero if they are NULL?
5 Answers
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Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign
...the issue. Removing this section and keeping the rest will still print the SQLite error being generated, which will note the column that has the problem.
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Sqlite primary key on multiple columns
What is the syntax for specifying a primary key on more than 1 column in SQLITE ?
9 Answers
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将 App Inventor 2 项目连接到外部传感器 · App Inventor 2 中文网
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ActiveRecord: List columns in table from console
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If you are comfortable with SQL commands, you can enter your app's folder and run rails db, which is a brief form of rails dbconsole. It will enter the shell of your database, whether it is sqlite or mysql.
Then, you can query the table columns using...
ALTER TABLE to add a composite primary key
...table you will get an error when trying to drop it. In some versions of mysql the error message there was malformed (as of 5.5.17, this error message is still
alter table parent drop column id;
ERROR 1025 (HY000): Error on rename of
'./test/#sql-a04_b' to './test/parent' (errno: 150).
If you wa...
When and why are database joins expensive?
...x strategy is available to the optimiser.
I used to be smarter than the MSSQL optimiser. That changed two versions ago. Now it generally teaches me. It is, in a very real sense, an expert system, codifying all the wisdom of many very clever people in a domain sufficiently closed that a rule-based s...