The method of mysql parallelism

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Mysql concurrency method: use the function [GROUP_CONCAT ()] with the code [SELECT am.activeId,GROUP_CONCAT (m.modelName SEPARATOR',') modelName].

The parallel method of mysql:

A field may correspond to multiple pieces of data. Use mysql to merge multiple rows of data into one row of data.

For example, an active id (activeId) corresponds to multiple module names (modelName), according to the general sql statement:

1 SELECT am.activeId,m.modelName 2 FROM activemodel am 3 JOIN model m 4 ON am.modelId = m.modelId 5 ORDER BY am.activeId

The list of queries is shown in figure 1:

Figure 1

The modified sql statement is shown in figure 2 after the query:

1 SELECT am.activeId,GROUP_CONCAT (m.modelName SEPARATOR',') modelName2 FROM activemodel am 3 JOIN model m 4 ON am.modelId=m.modelId5 WHERE m.valid=16 GROUP BY am.activeId

It is important to note:

The value in 1.GROUP_CONCAT () is the field name of the data you want to merge.

The SEPARATOR function is used to separate the data to be merged.

Which symbol do you want to use to separate it

two。 Grouping must be managed with GROUP BY statements, otherwise all data will be merged into a single record, as shown in figure 3

Figure 2

Figure 3

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