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MySQL InnoDB not releasing disk space after deleting data rows from table
I have one MySQL table using the InnoDB storage engine; it contains about 2M data rows. When I deleted data rows from the table, it did not release allocated disk space. Nor did the size of the ibdata1 file reduce after running the optimize table command.
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Compress files while reading data from STDIN
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This also works with xz: mysqldump mydb | xz > dbdump.sql.xz
– jeroen
Jul 27 '15 at 18:32
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MySQL - SELECT WHERE field IN (subquery) - Extremely slow why?
...and you only select indexed fields (and things are not too complex) than MySQL will resolve your query using only the indexes, speeding things way up.
General solution for 90% of your IN (select queries
Use this code
SELECT * FROM sometable a WHERE EXISTS (
SELECT 1 FROM sometable b
WHERE a...
How do I import CSV file into a MySQL table?
...normalized events-diary CSV from a client that I'm trying to load into a MySQL table so that I can refactor into a sane format. I created a table called 'CSVImport' that has one field for every column of the CSV file. The CSV contains 99 columns , so this was a hard enough task in itself:
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How can I append a string to an existing field in MySQL?
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You need to use the CONCAT() function in MySQL for string concatenation:
UPDATE categories SET code = CONCAT(code, '_standard') WHERE id = 1;
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How can I convert tabs to spaces in every file of a directory?
...bs everywhere in a file.
Will take a long time if you happen to have a 5GB SQL dump in this directory.
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Select row with most recent date per user
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Query:
SQLFIDDLEExample
SELECT t1.*
FROM lms_attendance t1
WHERE t1.time = (SELECT MAX(t2.time)
FROM lms_attendance t2
WHERE t2.user = t1.user)
Result:
| ID | USER | TIME | IO |
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Find the last element of an array while using a foreach loop in PHP
I am writing a SQL query creator using some parameters. In Java, it's very easy to detect the last element of an array from inside the for loop by just checking the current array position with the array length.
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Detect if a NumPy array contains at least one non-numeric value?
...arly oddness with NAN and boolen NULL is true in many languages, including SQL (where NULL=NULL is never true).
– user48956
Oct 4 '17 at 18:08
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Increment a value in Postgres
...olumns, 'name' and 'total', and Bill had a total of 203, what would be the SQL statement I'd use in order to move Bill's total to 204?
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