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SQL select only rows with max value on a column [duplicate]
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I know that MySQL allows you to add non aggregate fields to a "grouped by" query, but I find that kinda pointless. Try running this select id, max(rev), rev from YourTable group by id and you see what I mean. Take your time and try to un...
How to test an SQL Update statement before running it?
...What about Transactions? They have the ROLLBACK-Feature.
@see https://dev.mysql.com/doc/refman/5.0/en/commit.html
For example:
START TRANSACTION;
SELECT * FROM nicetable WHERE somthing=1;
UPDATE nicetable SET nicefield='VALUE' WHERE somthing=1;
SELECT * FROM nicetable WHERE somthing=1; #check
CO...
How do I select an entire row which has the largest ID in the table?
...show profiles and it appears our solutions have the same performance using MySQL. For my own knowledge, do you know what DBMS has poorer performance for subselects?
– unutbu
Feb 7 '14 at 20:08
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How to use JNDI DataSource provided by Tomcat in Spring?
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auth="Container"
type="javax.sql.DataSource"
driverClassName="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost:3306/TestDB"
username="pankaj"
password="pankaj123"
maxActive="100"
maxIdle="20"
minIdle="5"
maxWait="10000"/>
back to context.xml de spring add this
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How to add 'ON DELETE CASCADE' in ALTER TABLE statement
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Answer for MYSQL USERS:
ALTER TABLE ChildTableName
DROP FOREIGN KEY `fk_table`;
ALTER TABLE ChildTableName
ADD CONSTRAINT `fk_t1_t2_tt`
FOREIGN KEY (`parentTable`)
REFERENCES parentTable (`columnName`)
ON DELETE CASCADE
ON UP...
App Inventor 2 SQLite 拓展：超流行兼容主流SQL语法的迷你本地数据库引擎 ...
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SQLite 拓展
SQLite
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如何使用
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Spring Boot - Cannot determine embedded database driver class for database type NONE
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spring.datasource.url = jdbc:mysql://localhost/abc #spring.datasource.driverClassName = com.mysql.jdbc.Driver spring.datasource.name=olabsenglishdb spring.datasource.username=xxxx spring.datasource.password=xxxx spring.datasource.driver-class-name= com.m...
What are the use cases of Graph-based Databases (http://neo4j.org/)? [closed]
... team actually rewrote the database layer to use Oracle (or PostgreSQL, or MySQL), but it was slightly slower than the original. At least one large enterprise even had an Oracle-only policy, but luckily Oracle bought Berkeley DB. We also had to write a lot of extra tools - we couldn't just use Cryst...
JPA: unidirectional many-to-one and cascading delete
...solution to why delete was not working. apparently hibernate was NOT using mysql Engine -INNODB , you need engine INNODB for mysql to generate foreign key constraint. Using the following properties in application.properties, makes spring boot/hibernate to use mysql engine INNODB. So foreign key co...
ERROR 1452: Cannot add or update a child row: a foreign key constraint fails
I have created tables in MySQL Workbench as shown below :
21 Answers
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