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Cannot issue data manipulation statements with executeQuery()
...() to issue data manipulation statements. executeQuery() is only meant for SELECT queries (i.e. queries that return a result set).
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How do I use regex in a SQLite query?
...ite manager. You need to invoke it slightly differently though, like this: SELECT * FROM table WHERE column regexp("myregexp")
– Tristan
May 30 '14 at 17:16
...
How can I query a value in SQL Server XML column
...
select
Roles
from
MyTable
where
Roles.value('(/root/role)[1]', 'varchar(max)') like 'StringToSearchFor'
These pages will show you more about how to query XML in T-SQL:
Querying XML fields using t-sql
Flattening XML Dat...
How to convert number to words in java
...o use a built-in function of your DBMS (if available).
For Oracle
SQL> select to_char(to_date(873,'J'), 'JSP') as converted_form from dual;
CONVERTED_FORM
---------------------------
EIGHT HUNDRED SEVENTY-THREE
SQL>
'JSP' means :
J : the Julian format.
SP : spells the word for the number pa...
How to request a random row in SQL?
...
See this post: SQL to Select a random row from a database table. It goes through methods for doing this in MySQL, PostgreSQL, Microsoft SQL Server, IBM DB2 and Oracle (the following is copied from that link):
Select a random row with MySQL:
SELE...
Add Keypair to existing EC2 instance
...editing, or copying files that belong to non-root users. For example, your mysql user on instance A may have the same UID as your postfix user on instance B which could cause problems if you chown files with one name and then move the volume back to A.
Wrap Up
After you are done and you are happy ...
Finding duplicate values in a SQL table
...
SELECT
name, email, COUNT(*)
FROM
users
GROUP BY
name, email
HAVING
COUNT(*) > 1
Simply group on both of the columns.
Note: the older ANSI standard is to have all non-aggregated columns in the GROUP BY ...
内存优化总结:ptmalloc、tcmalloc和jemalloc - 操作系统(内核) - 清泛网 - ...
... 总共32个vcpu。 16个table，每个5M row。
OLTP_RO测试包含5个select查询：select_ranges, select_order_ranges, select_distinct_ranges, select_sum_ranges,
可以看到在多核心或者多线程的场景下， jemalloc和tcmalloc带来的tps增加非常明显。
参考资料
glibc...
How can I append a string to an existing field in MySQL?
... Alternatively you can use CONCAT_WS which skips NULL values. For example SELECT CONCAT_WS(', ','First name',NULL,'Last Name'); gives 'First name, Last Name'
– BarneySchmale
Aug 8 '16 at 11:00
...
Importance of varchar length in MySQL table
...
Anytime your select query uses a temporary table (group and order by operations, among other things) it will convert varchar(200) to a char(200) and performance will suffer.
– Jamie
Feb 7 '13 at 20:1...