how to use subquery in sql

.merchant_id=m.id) left join acquirer A on t_.acquirer_id = a.id) LEFT join acq_merchant am on t_.acq_merchant_id = am.id) LEFT JOIN Agency AG in m.agency_id = ag.id ORDER BY t.id desc where ID >0 limit 20;View mode:Local can be updated as long as the conditions of this view are satisfied;Cascaded must meet all of the view's criteria for the view to be updatedCREATE VIEW card as Select T.*,c.cardbin_name,c.issuer_name,t.cardbin_issuer_name,a.name Acquirer_name,m.merchant_ Name,am.merchant_name,t

First, group queryUse the group BY keyword to group data, use the HAVING keyword to set constraints on grouped data, and complete data grouping and statistics1.1 Aggregation functions: Often used to achieve data statistics functions①count () Statistics record number of records②sum () sum③min () to find the minimum value④max () to find the maximum value⑤avg () averagingExample: Query the average worker number for all employeesNote: The SELECT statement

CustomerID is an unrelated subquery 2, Hint (HINT) In general, the Oracle system optimizer determines the execution path of the statement, regardless of the rule-based or cost based approach, when optimizing. This path of choice is not necessarily the best. Therefore, Oracle provides a method called hint. It allows programmers to choose the execution path according to their requirements, which prompts the optimizer to follow the execution rule

I collected online materials and added my own SQL. 1. Group by is a group query. Generally, group by isUsed with aggregate Functions The principle of group by is that all columns after select do not use aggregate functions and must appear after group. 2. Having The where clause is used inBefore grouping query resultsRemove rows that do not meet the where condition, that is, filter data before groupi

t_policy_1_table are also scanned in the full table, so it is not slow. Then, the SQL filter condition has an in subquery.(SelectOrgan_idFrom t_company_organStart with organ_id = '123'Connect by prior organ_id = parent_id)In terms of the Execution Plan, CBO performs unnest on the son's query, because CBO generally thinks that the performance of the subquery is b

table are displayed in the order in which they are entered.The primary key features: Uniqueness, non-nullability.Example of setting a primary KEY statement:Code int primary Key, primary key cannot be empty, cannot be duplicated, ensures uniquenessExample of setting a self-growing primary KEY statement:Code int primary key identity (1), 1 increase each time, add values without adding this columnTo set a foreign key:Right-click on the table where you want to set the foreign key, select design, an

Briefly:In the query statement contains another query statement, the contained query is called a subquery, the query containing the subquery is called the parent query.In summary, a subquery is one or more query statements nested within a query statement. Common sub-query categories:One, independent sub-queryFeatures: S