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How to 'insert if not exists' in MySQL?
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Solution:
INSERT INTO `table` (`value1`, `value2`)
SELECT 'stuff for value1', 'stuff for value2' FROM DUAL
WHERE NOT EXISTS (SELECT * FROM `table`
WHERE `value1`='stuff for value1' AND `value2`='stuff for value2' LIMIT 1)
Explanation:
The innermost query
SELECT *...
Mysql: Select rows from a table that are not in another
How to select all rows in one table that do not appear on another?
8 Answers
8
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How do I check if a column is empty or null in MySQL?
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This will select all rows where some_col is NULL or '' (empty string)
SELECT * FROM table WHERE some_col IS NULL OR some_col = '';
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SELECT INTO Variable in MySQL DECLARE causes syntax error?
I´d like to SELECT a single value into a variable. I´d tried to following:
11 Answers
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MySQL maximum memory usage
...e to know how it is possible to set an upper limit on the amount of memory MySQL uses on a Linux server.
6 Answers
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What is the strict aliasing rule?
...mited buffer doesn't necessarily help.
So how do I get around this?
Use a union. Most compilers support this without complaining about strict aliasing. This is allowed in C99 and explicitly allowed in C11.
union {
Msg msg;
unsigned int asBuffer[sizeof(Msg)/sizeof(unsigned int)];
};
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Why do we need C Unions?
When should unions be used? Why do we need them?
18 Answers
18
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Select all columns except one in MySQL?
I'm trying to use a select statement to get all of the columns from a certain MySQL table except one. Is there a simple way to do this?
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How to best display in Terminal a MySQL SELECT returning too many fields?
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Terminate the query with \G in place of ;. For example:
SELECT * FROM sometable\G
This query displays the rows vertically, like this:
*************************** 1. row ***************************
Host: localhost
Db: mydatabase1
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How do I connect to a MySQL Database in Python?
...ueries you need
cur = db.cursor()
# Use all the SQL you like
cur.execute("SELECT * FROM YOUR_TABLE_NAME")
# print all the first cell of all the rows
for row in cur.fetchall():
print row[0]
db.close()
Of course, there are thousand of possibilities and options; this is a very basic example. Y...