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How to drop unique in MySQL?
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Simply you can use the following SQL Script to delete the index in MySQL:
alter table fuinfo drop index email;
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MIN/MAX vs ORDER BY and LIMIT
... faster in the worst case, indistinguishable in the best case, is standard SQL and most clearly expresses the value you're trying to get. The only case where it seems that using SORT and LIMIT would be desirable would be, as mson mentioned, where you're writing a general operation that finds the to...
API pagination best practices
...just an incrementing number and does not preserve a date or a time. ... In SQL server 2008 and later, the timestamp type has been renamed to rowversion, presumably to better reflect its purpose and value." So there's no evidence here that timestamps (those that actually contain a time value) are uni...
MongoDB vs. Cassandra [closed]
...mentation; Cassandra provides native Hadoop support, including for Hive (a SQL data warehouse built on Hadoop map/reduce) and Pig (a Hadoop-specific analysis language that many think is a better fit for map/reduce workloads than SQL). Cassandra also supports use of Spark.
Not worried about "massiv...
Using current time in UTC as default value in PostgreSQL
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FWIW, running this query in PostgreSQL 11.5: ALTER TABLE testcase_result ADD COLUMN date_created TIMESTAMP WITHOUT TIME ZONE DEFAULT (NOW() AT TIME ZONE "UTC") NOT NULL; fails with: ERROR: column "UTC" does not exist. Make sure 'utc' is all lower-case.
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MySQL Results as comma separated list
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The intent is fine and MySQL will allow this, but be careful (generally) with your use of GROUP BY. The items in the select list need to be valid aggregates in the context of the GROUP BY clause. In this case, p.name is not strictly valid. Any dat...
Closing JDBC Connections in Pool
...synchronization nor nullchecks.
See also:
Is it safe to use a static java.sql.Connection instance in a multithreaded system?
Am I Using JDBC Connection Pooling?
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Good tool to visualise database schema? [closed]
...any good tools for visualising a pre-existing database schema? I'm using MySQL if it matters.
20 Answers
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How to add an auto-incrementing primary key to an existing table, in PostgreSQL?
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(Updated - Thanks to the people who commented)
Modern Versions of PostgreSQL
Suppose you have a table named test1, to which you want to add an auto-incrementing, primary-key id (surrogate) column. The following command should be sufficient in recent versions of PostgreSQL:
ALTER TABLE test1 A...
“INSERT IGNORE” vs “INSERT … ON DUPLICATE KEY UPDATE”
...ut the values you insert don't map to a partition.
If you use REPLACE, MySQL actually does a DELETE followed by an INSERT internally, which has some unexpected side effects:
A new auto-increment ID is allocated.
Dependent rows with foreign keys may be deleted (if you use cascading foreign keys...