Single Standard Query
Implementation of priority keywords
LIMIT query to limit the number of records
Using regular expressions inquiry
SELECT DISTINCT Field 1, Field ... 2 the FROM table
WHERE conditions for
the GROUP BY Field,
the HAVING screening
the ORDER BY Field,
LIMIT limit the number of
Implementation of priority keywords
from where Group by SELECT DISTINCT HAVING Order by limit
1. Table Found : from
2. holding where specified constraints, to the file / table records an extraction
3. a group of records retrieved Group by , if not by group , a group of the entirety
4. this line SELECT (de-emphasis)
5. the result of the grouping is having filter
6. the results are sorted by the condition: Order by
7. the result limit the number display bar
# Simple query select field names, field names, field names from the table name ---- name query select * from table name ----- Search # avoid duplication DISTINCT select DISTINCT field name from the table name; # define the display format concat () function is used to string SELECT the concat ( " name: " field name) from name; first parameter CONCAT_WS () is a separation line SELECT CONCAT_WS ( ' : ' , field name) from name; # by four operation query select field names, salary * 12 (salary * 12) as annual_salary (salary) from the table name # operation plus redefine name
where words can be used:
1. The comparison operators:> <> = <= <>! =
2.between 80 and 100 # value between 80 and 100
3.in (80,10) # value of 80 or 10
4.like 'e%'
Wildcards can be a% or _,
% Represents any number of characters
_ Represents one character
The logical operators and or not
# Single condition search select field names from table where conditions; Example: select the emp_name from Employee where POST = ' Sale ' ; # many conditions select field names from Employee where conditions and conditions of Example: the SELECT the emp_name, the salary the FROM Employee the WHERE POST = ' Teacher ' the aND the salary> 10000 ; # key between and Example: the emp_name the SELECT, the salary the FROM Employee the WHERE the salary the BETWEEN 10000 the aND 20000 ; the SELECT the emp_name, the salary the FROM Employee the WHERE the salary the NOT the BETWEEN 10000 20000 the aND; # Keywords IS NULL (null determines whether or not a field equal sign, need IS) Example: the emp_name the SELECT, the post_comment the FROM Employee the WHERE the post_comment the IS NULL; the SELECT the emp_name, the post_comment the FROM Employee the WHERE the post_comment the IS the NOT NULL; note the empty string is not null # keyword IN collection query Example: the emp_name the SELECT, the salary the FROM Employee the WHERE the salary = the salary = 3000 OR 3500 OR 4000 OR = the salary the salary = 9000 ; the SELECT the emp_name, the salary the FROM Employee the WHERE IN the salary ( 3000,3500 , 4000,9000 ); the SELECT emp_name, the Employee salary the FROM the WHERE salary the NOT the IN ( 3000,3500,4000,9000 ); # keywords like fuzzy query 例: 通配符’%’ SELECT * FROM employee WHERE emp_name LIKE 'eg%'; 通配符’_’ SELECT * FROM employee WHERE emp_name LIKE 'al__';
# Alone group by grouping keyword SELECT POST from Employee group by POST; # group by keywords and GROUP_CONCAT () function used in conjunction SELECT POST, GROUP_CONCAT (the emp_name) from Employee group by POST; # accordance job packet, and the query groups member name # Group by using aggregate functions with the SELECT POST, COUNT (the above mentioned id) from the Employee Group by POST; # accordance job grouping, and see how many of each there are '' ' stressed: if we use the field as a unique basis for grouping , each self-contained record set, this packet is not sense the same value between a field of a plurality of records, this field is generally used as the basis of a packet '' '
# Emphasized: aggregation function polymerized content set, if no packet, a set of default Example: the SELECT COUNT ( * ) the FROM Employee; the SELECT COUNT ( *) the FROM Employee the WHERE depart_id =. 1 ; the SELECT MAX (the salary) the FROM Employee; MIN the SELECT (the salary) the FROM Employee; the SELECT the AVG (the salary) the FROM Employee; the SELECT the SUM (the salary) the FROM Employee; the SELECT the SUM (the salary) the WHERE depart_id the FROM Employee =. 3;
HAVING and WHERE is not the same place !!!!!! # ! ! ! Execution priority from high to low: WHERE> Group by> HAVING # 1. Where occurs before the packet group by, and thus there can Where any field, but must not use the aggregate functions. # 2. Having occurs after a packet group by, Having thus can be used in the field of the packet, can not be taken directly to other fields, aggregate functions can be used
mysql> select @@sql_mode; +--------------------+ | @@sql_mode | +--------------------+ | ONLY_FULL_GROUP_BY | +--------------------+ row in set (0.00 sec) mysql> select * from emp where salary > 100000; +----+------+------+-----+------------+---------+--------------+------------+--------+-----------+ | id | emp_name | sex | age | hire_date | post | post_comment | salary | office | depart_id | +----+------+------+-----+------------+---------+--------------+------------+--------+-----------+ | 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 | +----+------+------+-----+------------+---------+--------------+------------+--------+-----------+ row in set (0.00 sec) mysql> select post,group_concat(emp_name) from emp group by post having salary > 10000;#错误，分组后无法直接取到salary字段 ERROR 1054 (42S22): Unknown column 'salary' in 'having clause' mysql> select post,group_concat(emp_name) from emp group by post having avg(salary) > 10000; + ----------- + ------------------------------------- ------------------ + | post | group_concat(emp_name) | + ----------- + ------------------------------------- + ------------------ | Operation | process bite iron, copper bite Cheng Cheng bite silver, Yaojin, Zhang Ye | | Teacher | Chan, jinxin, jingliyang, liwenzhou, yuanhao, wupeiqi, alex | + ----------- + ----------------------------- + -------------------------- rows in the SET (0.00 sec) verification
Press single sort the SELECT * the FROM Employee the ORDER BY the salary; the SELECT * the FROM Employee the ORDER BY the salary the ASC; # ascending the SELECT * the FROM Employee the ORDER BY the salary DESC; # descending by multiple column sort: first according to age ordering, if older the same, according to payroll Sort the SELECT * from the Employee the ORDER BY Age, salary DESC;
LIMLT limit the number of records the query
Example: the SELECT * the FROM Employee the ORDER BY DESC the salary the LIMIT . 3; # default initial position is 0 the SELECT * the FROM Employee the ORDER BY DESC the salary the LIMIT 0, . 5; # starts from 0, i.e., the first query first, then this one comprising including five check back the SELECT * the fROM the Employee the ORDER BY salary DESC LIMIT 5,5; # from the beginning of the fifth, which is to check out the article 6, which then contains a later investigation, including 5
Using regular expressions inquiry
The SELECT * the FROM Employee the WHERE the emp_name REGEXP, ' ^ ale ' ; # In ale begin the SELECT * the FROM Employee the WHERE the emp_name REGEXP, ' on $ ' ; # in on the end of the SELECT * the FROM Employee the WHERE the emp_name REGEXP, ' m {2} ' ; # two consecutive a m