select count distinct

Document directory Use bulk collect to reduce loop processing overhead Oracle batch binding forall bulk collect Use bulk collect to improve Oracle query efficiency Bulk collect can be used to reduce the overhead of loop processing. Bulk collect

Select * From t_tag_source where s_name = 'hao123 '; + -------- + ---------- + --------- + -------- + --------- + ------------ + ---------- +| S_name | s_fname | s_level | tag_id | tag_fid | author | updatetime | level_1_id | level_2_id | level_3_id

50 commonly used test and interview SQL statements Postedon50 commonly used test and interview SQL statements 2009-12-1715: 05 Student (S #, Sname, Sage, Ssex) student table Course (C #, Cname, T #) Course list SC (S #, C #, score) Instructor table

In pinwu performance optimization, Chapter 4.4.3 describes the two features of composite indexes: prefix and optionality. What is prefix? The book explains how to exclude skip scan index (there are not many pre-index columns, such as gender). If the

Today, my friend asked a particularly tangled question: In a table in the database, the table duplicates a field in the table and sorts the remaining data according to another field, Create a table as follows: Create table TEST_DISTINCT (ID integer

MySQL Group By optimization I wrote a blog post on MySQL's loose index scan (). Later I found that the main purpose of the optimization method mentioned last time was to implement loose index scan, at the execution plan level, the Extra information

Comparison and usage of distinct and group by statements in MySQL, mysqldistinct The data table records the bibliography used for user verification. Now I want to retrieve all the bibliography and use DISTINCT and group by to get the expected

50 SQL statements involved in one question Student (s #, sname, sage, ssex) Student tableCourse (C #, cname, T #) CurriculumSC (s #, C #, score) Orders tableTeacher (T #, tname) Instructor table Problem:1. query the student ID of all students

Summary of Row-to-column conversion problems-1. Row-to-column conversion (various problems in the forum will be sorted out later) --- 1. Simplest row-to-column Conversion/* Question: Suppose there is a student orders table (TB) as follows:Name

Summary of Row-to-column conversion problems-1. Row-to-column conversion (various problems in the forum will be sorted out later) --- 1. Simplest row-to-column Conversion/* Question: Suppose there is a student orders table (TB) as follows:Name

Preface when you perform Mysql Data Analysis Online, you may encounter the situation of importing SQL files to the MySQL database by executing shell scripts or connecting MySQL to execute specified SQL statements, here we will introduce how to

SQL advanced (9) functions, SQL FunctionsSQL advanced (9) function syntax built-in SQL function syntax is: SELECT function (column) FROM tableIn SQL, there are several basic function types and types. The basic types of functions are: Aggregate

Mysql column-to-row and year-to-year group bitsCN.com Mysql column-to-row and month-to-month grouping Java code SELECT count (DISTINCT (. rect_id) zcount,. job_dept, DATE_FORMAT (submit_date, '% Y-% M') zsubmit_date FROM table name a WHERE. statu

Mysql month/year grouping statement bitsCN.com Mysql grouping statement Java code SELECT count (DISTINCT (a. rect_id) zcount, a. job_dept, DATE_FORMAT (submit_date, '% Y-% M') zsubmit_date FROM Table name WHERE A. statu = 3 AND a. rstatu = 2 AND a.

--Query month service days are not equal to the number of month service days stored in the databaseSelect B.day1,a.days_of_month from Erp_work_day_opt_info_copy A, (select count (DISTINCT service_day) as Day1, order_id From

This article describes how to use the showprofile command in MySQL to analyze performance. showprofiles is a common command for database performance optimization, for more information, see how to donate the show profile to the MySQL community by

In the following code, how to filter html such as htmlentities () is to filter the keyword, that is, to filter out the html code from the search content entered by the user If you have trouble, give the code directly. The younger brother doesn't

This article mainly introduces the comparison and usage of distinct and groupby in MySQL. There are many similarities between the two in query operations, if you need a friend, you can refer to the bibliography recorded in the data table for user

function Get_shijian_list ($school _id, $parent _id) { $sql = "Select Shijian_id,name,type from". $fdyu->table (' Oa_shijian '). "Where parent_id=". $parent _id. "and school_id = ". $school _id." ORDER by shijian_id ASC "; $res = $db->query ($sql); $

6.1 SELECT ... From statementhive> SELECT name,salary from employees;--General Queryhive>select e.name, e.salary from Employees e;--alias query is also supported when a user selects a column that is a collection data type, Hive uses JSON syntax to