CPDA|How Operators Learn Data Analysis (SQL) from Negative Foundations

CPDA|How operators learn data analysis (SQL) from negative foundations

Every newcomer will realize that operation is a job that does not seem to have its own core competitiveness and sense of security.Because every day's work seems to be surrounded by all kinds of trivial matters, and there is only one theme that is eternal, that is - raising needs, constantly raising various needs.
Operators need a hard core skill to enhance their professional value and improve their sense of occupational security, instead of waiting for various scheduling every day: data analysis scheduling, product design scheduling, UI scheduling,Development schedule.
Operations urgently need to use SQL tools to discover more business value from data in time and improve their output.

SQL is probably the most and most important tool used by Internet companies for data analysis. In the entire data analysis process, using SQL to extract data may account for 50%-80% of the entire data analysis process.As for many data analysts, they are nicknamed "Sql Boy/Girl".

The function of the mysql database can be summed up in four words: additions, deletions, changes, and inquiries.
But for us, we can only use the database query function, other permissions are impossible to open to you.

If you think the database is jerky, you can understand it like this:
•SQL?Is an order to access data
• Database?It's like a folder
•Datasheets?It is equivalent to an Excel file in the folder
– the table name is the file name
– each column in the table has a name, which is the column name, and can also be a field

SQL learning can be divided into three parts:
simple query,
associated query,
function reference.

What is a query?
After the database is established, through the most commonly used statement SELECT in the sql command, let us view the data saved in the database, and can conduct certain analysis and induction.

Simple query:
The complete format of the SELECT statement includes 6 clauses:
1. FROM clause: query the table of data and specify the source of the data.
2. WHERE clause: filter conditions for query data.
3. GROUP BY clause: Group the query results matching the WHERE clause.
4. HAVING clause: Condition the grouped results.
5. ORDER BY clause: sort the query results, followed by DESC descending or ASC ascending (default).
6, LIMIT clause: limit the number of rows in the displayed results of the query.

Associated query:
If you want to query multiple tables, you need to use a connection.
Join query is to join two or more tables together to obtain data, which is the most important query in relational database.The connection methods of tables mainly include inner join, outer join and cross join.
1. From specifies the query table name and gives an alias.
2, left join left outer join, all records in the left table and matching records in the right table appear in the query results.
3, inner join inner join, the common records of the left table and the right table appear in the query results.
4, right join right outer join, all records in the right table and matching records in the left table appear in the query results.
5. on Specify the associated conditions.
The result of table join can be clearly displayed by the graph.

Function reference:
The use of functions can improve the efficiency of sql. The most commonly used functions are:
Logical operations: and, or, not;
Numerical operations: round, floor, ceil, rand, exp, sqrt, etc.;
Date functions: from_unixtime, unix_timestamp, year, month, day, hour, minute, second, weekofyear, detediff, date_add, date_sub, etc.;
Conditional functions: if, coalesce, case when, etc.;
String functions: concat, substr, trim, reverse, split, etc.;
Set statistics functions: count, sum, max, min, percentile, etc.