【 Abstract 】
When selecting data from a data table , Sometimes it is necessary to judge whether members exist under certain conditions , These conditions may be queried from other data tables . For example, a score is a field in a grade sheet , How to choose from the student list that each subject score is higher than 80 The students of grade ？ How to deal with the problem of judging the existence of structured data easily and quickly , Here's the whole process , And provide esProc Sample code . The problem of existence judgment in structured data
1. Detection of the existence of foreign key mappings
In two tables , Find records based on the existence of the foreign key mapping .
【 example 1】 Count the average score of boys in class one . The grade and student charts are as follows ：
【 Their thinking 】
When selecting data from the score table , Judge whether there is a record that the class name is a class and the student's gender is male , If there is, choose .
【SPL Script 】
A6 The results are as follows ：
When the foreign key table has a large amount of data , You can use an ordered merge of cursors to solve .
【 example 2】 Inquire about 2014 The number of orders without discount per month . The order list and order details are as follows ：
【 Their thinking 】
When selecting data from the order form , Judge whether there is discount for 0 The order of , If there is, choose .
【SPL Script 】
A6 The results are as follows ：
2. Detection of the existence of non equivalent connections
In a table , Find data by detecting the existence of non equivalent links .
【 example 3】 Query the sales volume of orders with the same order span more than one year . Part of the order form is as follows ：
【 Their thinking 】
When selecting data from the order table , Judge whether the records with order span more than one year exist , If there is, choose .
【SPL Script 】
A5 The results are as follows ：
3. Nonexistence detection of foreign key mapping
In two tables , Find records based on nonexistence detection of foreign key mapping .
【 example 4】 All subjects are higher than 80 The students of grade . The grade and student charts are as follows ：
【 Their thinking 】
When selecting data from the student table , Judge whether any subject is lower than 80 Points of , If not, choose .
【SPL Script 】
A6 The results are as follows ：
4. The existence test of double negation
Through double negation , Query records that can match .
【 example 5】 Check the students who have taken all courses . Course selection table 、 The curriculum and student schedule are as follows ：
【 Their thinking 】
When selecting data from the student table , Judge whether the student has a record that is not selected in the course of a certain subject , If not, choose . When dealing with the existence detection of double negation , We can also think positively , Just select a record with the same number of elective subjects as all subjects .
【SPL Script 】
A7 The results are as follows ：
5. Detection of the existence of arbitrary conditions
In two tables , Find records according to the existence of any condition .
【 example 6】 The score difference between the two subjects is more than 30 The students of grade . The grade and student charts are as follows ：
【SQL sentence 】
When selecting data from the student table , Judge whether there is any difference between the scores of any two subjects 30 A minute's record , Choose if you exist .
【SPL Script 】
A7 The results are as follows ：
6. Detection of the existence of all conditions
According to the data in a table , Filter out records that meet all criteria .
【 example 7】 Find out which employees are paid more than all sales employees . Some of the data in the employee table are as follows ：
【SQL sentence 】
When selecting data from the employee table , Judge whether there is a record that the employee's salary is greater than that of all employees in the sales department , Choose if you exist .
【SPL Script 】
A4 The results are as follows ：
《SPL CookBook》 There are more examples of relevant calculations in .
