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MYSQL OR vs IN performance
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Performance reason (quoting MariaDB(a MySQL new free branch) docs): Returns 1 if expr is equal to any of the values in the IN list, else returns 0. If all values are constants, they are evaluated according to the type of expr and sorted. The search for the item t...
How can I get enum possible values in a MySQL database?
...wns with enum possible values from a DB automatically. Is this possible in MySQL?
24 Answers
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Is there a MySQL command to convert a string to lowercase?
I have a MySQL database of keywords that are presently mixed-case. However, I want to convert them all to lowercase. Is there an easy command to do this, either using MySQL or MySQL and PHP?
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MySQL: Fastest way to count number of rows
Which way to count a number of rows should be faster in MySQL?
12 Answers
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App Inventor 2 列表代码块 · App Inventor 2 中文网
...用给定的变量名称 item 来引用当前列表项。
此处 是有关如何使用该块的教程。
创建过滤列表
通过保持输入列表中的每个项目满足测试来创建一个新列表。
主体是一个布尔表达式，用于检查项目是否通过...
Delete all Duplicate Rows except for One in MySQL? [duplicate]
How would I delete all duplicate data from a MySQL Table?
2 Answers
2
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How do I change the data type for a column in MySQL?
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http://dev.mysql.com/doc/refman/5.1/en/alter-table.html
ALTER TABLE tablename MODIFY columnname INTEGER;
This will change the datatype of given column
Depending on how many columns you wish to modify it might be best to generate a scri...
Are duplicate keys allowed in the definition of binary search trees?
...a BST which allows either of the right or left children to be equal to the root node, will require extra computational steps to finish a search where duplicate nodes are allowed.
It is best to utilize a list at the node to store duplicates, as inserting an '=' value to one side of a node requires r...
How do I update if exists, insert if not (AKA “upsert” or “merge”) in MySQL?
...SERT a row when it does not exist, or to UPDATE if it exists, using one MySQL query?
2 Answers
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MySQL Creating tables with Foreign Keys giving errno: 150
I am trying to create a table in MySQL with two foreign keys, which reference the primary keys in 2 other tables, but I am getting an errno: 150 error and it will not create the table.
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