1. Aggregation function

1. Commonly used aggregation functions

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2. Examples

（1）count

Count the number of students in the class.

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Count the number of qq numbers collected by the class.
Before doing this requirement, we first create a table and insert certain data as shown in the figure below:

Now let's check how many qq numbers there are. As can be seen from the above figure, there are a total of 3 qq numbers.

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（2）sum

The total score of the statistical mathematics achievement.
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（3）avg

The average score of the total scores of the three subjects of Chinese, Mathematics and English in the statistical score sheet.
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（4）max

Returns the highest score for the English score.
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（5）min

Returns > 70+ minimum score in mathematics
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2. Built-in functions

1. Date function

(1) Overview

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(2) Example

Obtain year, month, day:
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Obtain hour, minute, second:

Obtain timestamp:

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Add a date to a date:

Subtract a date from a date:

Calculate the difference in days between two dates:

(3) Case

Let's first create a birthday table:
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We then insert the data into the table with the current date as the birthday.
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2. String functions

(1) Overview

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(2) Example

Get the character set of the name of the exam_result table.
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It is required to display the information in the exam_result table, and the display format is: "XXX has XXX points in Chinese, and XXX points in mathematics."

Replace all names with "Tang" in the exam_result table with "Beijing".