I am using MySQL 5.1. As a rookie, here are some basic command commands I feel useful to rememberknow.
Some basic mysql commands
Use mysql client to access the database.
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% $ myslq -u database-user -p |
Show databases
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mysql> SHOW FULL PROCESSLIST; |
Some useful SQL commands
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Find Duplicates of a field set
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mysql> select *, count(*) as count from table-name group by field1, field2, ... having count(*) >1; |
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Get median generally
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There are some useful group by functions in MySQL, like avg(), std(), max() and so on, but there is not a median function. Following SQL statement is a general way to achieve this purpose
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SELECT m.name, avg(m.medians) medians from ( SELECT x.name, x.val medians FROM A x, A y WHERE x.name=y.name GROUP BY x.name, x.val HAVING SUM(y.val <= x.val) >= COUNT(*)/2 AND SUM(y.val >= x.val) >= COUNT(*)/2 )AS m group by m.name; |
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Save SQL results in a csv file,
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SELECT ...
FROM ...
INTO OUTFILE '/tmp/sqlresults.csv'
FIELDS TERMINATED BY ','
OPTIONALLY ENCLOSED BY '"'
ESCAPED BY '\\'
LINES TERMINATED BY '\n';
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