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MySQL Creating tables with Foreign Keys giving errno: 150
...h a value in the Parent table PK column(s). Check this with a query like:
SELECT COUNT(*) FROM Child LEFT OUTER JOIN Parent ON Child.FK = Parent.PK
WHERE Parent.PK IS NULL;
This must return zero (0) unmatched values. Obviously, this query is an generic example; you must substitute your table nam...
Real escape string and PDO [duplicate]
...ing. So if people are building out queries that already have quotes like "SELECT * FROM users WHERE username = '".$conn->quote($username)."'";, the queries will inevitably fail.
– user1669496
Jun 11 '14 at 18:05
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GROUP_CONCAT ORDER BY
...
You can use ORDER BY inside the GROUP_CONCAT function in this way:
SELECT li.client_id, group_concat(li.percentage ORDER BY li.views ASC) AS views,
group_concat(li.percentage ORDER BY li.percentage ASC)
FROM li GROUP BY client_id
...
Citrix服务器虚拟化：XenApp 6.5发布服务器上的应用程序 - 更多技术 - 清泛...
...的其他应用程序旁边。用户无须了解应用程序在何处以及如何执行。
8) 脱机访问:配置并交付之后，应用程序在断开网络连接后也可供用户使用。
9) 易于灾难恢复:按需应用程序交付对灾难恢复状况而言是一个强大的概念，...
MySQL Removing Some Foreign keys
...
You can use this to find foreign key constraints: SELECT * FROM information_schema.table_constraints WHERE constraint_schema = '<your db name>' AND constraint_type = 'FOREIGN KEY'
– Gayan Dasanayake
Aug 26 '17 at 2:48
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MySQL: Sort GROUP_CONCAT values
... see http://dev.mysql.com/doc/refman/...tions.html#function_group-concat:
SELECT student_name,
GROUP_CONCAT(DISTINCT test_score ORDER BY test_score DESC SEPARATOR ' ')
FROM student
GROUP BY student_name;
share
...
What is the difference between BIT and TINYINT in MySQL?
...deployed everything on linux, I had problems with queries that inserted or selected from tables that had BIT DATA TYPE.
Bit is not safe for now.
I changed to tinyint(1) and worked perfectly. I mean that you only need a value to diferentiate if it's 1 or 0 and tinyint(1) it's ok for that
...
Does MySQL ignore null values on unique constraints?
... '1' for key 'x'
INSERT table1 VALUES (NULL);
INSERT table1 VALUES (NULL);
SELECT * FROM table1;
Result:
x
NULL
NULL
1
This is not true for all databases. SQL Server 2005 and older, for example, only allows a single NULL value in a column that has a unique constraint.
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Add list to set?
...
With respect to sets, the | operator implements the set union operation. Both the |= operator and set.update() method apply that operation in-place and are effectively synonymous. So, set_a |= set_b could be considered syntactic sugar for both set_a.update(set_b) and set_a = set_a...
How to select all records from one table that do not exist in another table?
...
SELECT t1.name
FROM table1 t1
LEFT JOIN table2 t2 ON t2.name = t1.name
WHERE t2.name IS NULL
Q: What is happening here?
A: Conceptually, we select all rows from table1 and for each row we attempt to find a row in table2 wi...