大约有 47,000 项符合查询结果（耗时：0.0173秒） [XML]
Why is SELECT * considered harmful?
Why is SELECT * bad practice? Wouldn't it mean less code to change if you added a new column you wanted?
15 Answers
...
How to select only date from a DATETIME field in MySQL?
...e a table in the MySQL database that is set up with DATETIME . I need to SELECT in this table only by DATE and excluding the time.
...
How to declare a variable in MySQL?
...at has not been
initialized, it has a value of NULL and a type of string.
SELECT @var_any_var_name
You can initialize a variable using SET or SELECT statement:
SET @start = 1, @finish = 10;
or
SELECT @start := 1, @finish := 10;
SELECT * FROM places WHERE place BETWEEN @start AND @finish...
How to select unique records by SQL
When I perform "SELECT * FROM table" I got results like below:
8 Answers
8
...
What is the “N+1 selects problem” in ORM (Object-Relational Mapping)?
The "N+1 selects problem" is generally stated as a problem in Object-Relational mapping (ORM) discussions, and I understand that it has something to do with having to make a lot of database queries for something that seems simple in the object world.
...
Export database schema into SQL file
...ht click the database you want to generate scripts for (not the table) and select tasks - generate scripts
Next, select the requested table/tables, views, stored procedures, etc (from select specific database objects)
Click advanced - select the types of data to script
Click Next and finish
MSDN...
MySQL select 10 random rows from 600K rows fast
How can I best write a query that selects 10 rows randomly from a total of 600k?
26 Answers
...
How to get multiple counts with one SQL query?
...tion. This is basically the same thing as a PIVOT function in some RDBMS:
SELECT distributor_id,
count(*) AS total,
sum(case when level = 'exec' then 1 else 0 end) AS ExecCount,
sum(case when level = 'personal' then 1 else 0 end) AS PersonalCount
FROM yourtable
GROUP BY distributor_id
...
How to select only 1 row from oracle sql?
I want to use oracle syntax to select only 1 row from table DUAL . For example, I want to execute this query:
13 Answers
...
MySQL: Insert record if not exists in table
...oDB;
Insert a record:
INSERT INTO table_listnames (name, address, tele)
SELECT * FROM (SELECT 'Rupert', 'Somewhere', '022') AS tmp
WHERE NOT EXISTS (
SELECT name FROM table_listnames WHERE name = 'Rupert'
) LIMIT 1;
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0
...