inner-join | 易学教程

MySQL INNER JOIN select only one row from second table

阅读更多关于 MySQL INNER JOIN select only one row from second table

问题 I have a users table and a payments table, for each user, those of which have payments, may have multiple associated payments in the payments table. I would like to select all users who have payments, but only select their latest payment. I'm trying this SQL but i've never tried nested SQL statements before so I want to know what i'm doing wrong. Appreciate the help SELECT u.* FROM users AS u INNER JOIN ( SELECT p.* FROM payments AS p ORDER BY date DESC LIMIT 1 ) ON p.user_id = u.id WHERE u

WHERE Clause vs ON when using JOIN

阅读更多关于 WHERE Clause vs ON when using JOIN

Assuming that I have the following T-SQL code: SELECT * FROM Foo f INNER JOIN Bar b ON b.BarId = f.BarId; WHERE b.IsApproved = 1; The following one also returns the same set of rows: SELECT * FROM Foo f INNER JOIN Bar b ON (b.IsApproved = 1) AND (b.BarId = f.BarId); This might not be the best case sample here but is there any performance difference between these two? No, the query optimizer is smart enough to choose the same execution plan for both examples. You can use SHOWPLAN to check the execution plan. Nevertheless, you should put all join connection on the ON clause and all the

How to use mysql JOIN without ON condition?

阅读更多关于 How to use mysql JOIN without ON condition?

Is it possible to write join query without ON statement? and how do these joins differ LEFT JOIN, RIGHT JOIN works. MySQL documentation covers this topic. Here is a synopsis. When using join or inner join , the on condition is optional. This is different from the ANSI standard and different from almost any other database. The effect is a cross join . Similarly, you can use an on clause with cross join , which also differs from standard SQL. A cross join creates a Cartesian product -- that is, every possible combination of 1 row from the first table and 1 row from the second. The cross join for

MySQL: Inner join vs Where [duplicate]

阅读更多关于 MySQL: Inner join vs Where [duplicate]

问题 This question already has an answer here: Explicit vs implicit SQL joins 12 answers Is there a difference in performance (in mysql) between Select * from Table1 T1 Inner Join Table2 T2 On T1.ID = T2.ID And Select * from Table1 T1, Table2 T2 Where T1.ID = T2.ID ? 回答1: As pulled from the accepted answer in question 44917: Performance wise, they are exactly the same (at least in SQL Server) but be aware that they are deprecating the implicit outer join syntax. In MySql the results are the same.

Mixing ANSI 1992 JOINs and COMMAs in a query

阅读更多关于 Mixing ANSI 1992 JOINs and COMMAs in a query

i'm trying the following MySQL query to fetch some data: SELECT m.*, t.* FROM memebers as m, telephone as t INNER JOIN memeberFunctions as mf ON m.id = mf.memeber INNER JOIN mitgliedTelephone as mt ON m.id = mt.memeber WHERE mf.function = 32 But i always get the following error: #1054 - Unknown column 'm.id' in 'on clause' The column does exists and the query works fine with only one table (e.g. when i remove telephone) Does anybody know what I do wrong? It seems your requirement is to join members table but you are joining with telephone table. just change their order. SELECT `m`.*, `t`.*

Is having an 'OR' in an INNER JOIN condition a bad idea?

阅读更多关于 Is having an 'OR' in an INNER JOIN condition a bad idea?

In trying to improve the speed of an immensely slow query (several minutes on two tables with only ~50,000 rows each, on SQL Server 2008 if it matters), I narrowed down the problem to an OR in my inner join, as in: SELECT mt.ID, mt.ParentID, ot.MasterID FROM dbo.MainTable AS mt INNER JOIN dbo.OtherTable AS ot ON ot.ParentID = mt.ID OR ot.ID = mt.ParentID I changed this to (what I hope is) an equivalent pair of left joins, shown here: SELECT mt.ID, mt.ParentID, CASE WHEN ot1.MasterID IS NOT NULL THEN ot1.MasterID ELSE ot2.MasterID END AS MasterID FROM dbo.MainTable AS mt LEFT JOIN dbo

Eliminating duplicate values based on only one column of the table

阅读更多关于 Eliminating duplicate values based on only one column of the table

问题 My query: SELECT sites.siteName, sites.siteIP, history.date FROM sites INNER JOIN history ON sites.siteName = history.siteName ORDER BY siteName,date First part of the output: How can I remove the duplicates in siteName column? I want to leave only the updated one based on date column. In the example output above, I need the rows 1, 3, 6, 10 回答1: This is where the window function row_number() comes in handy: SELECT s.siteName, s.siteIP, h.date FROM sites s INNER JOIN (select h.*, row_number()

Difference in MySQL JOIN vs LEFT JOIN

阅读更多关于 Difference in MySQL JOIN vs LEFT JOIN

问题 I have this cross-database query... SELECT `DM_Server`.`Jobs`.*, `DM_Server`.servers.Description AS server, digital_inventory.params, products.products_id, products.products_pdfupload, customers.customers_firstname, customers.customers_lastname FROM `DM_Server`.`Jobs` INNER JOIN `DM_Server`.servers ON servers.ServerID = Jobs.Jobs_ServerID JOIN `cpod_live`.`digital_inventory` ON digital_inventory.jobname = Jobs.Jobs_Name JOIN `cpod_live`.`products` ON products.products_pdfupload = CONCAT

How to use mysql JOIN without ON condition?

阅读更多关于 How to use mysql JOIN without ON condition?

问题 Is it possible to write join query without ON statement? and how do these joins differ LEFT JOIN, RIGHT JOIN works. 回答1: MySQL documentation covers this topic. Here is a synopsis. When using join or inner join , the on condition is optional. This is different from the ANSI standard and different from almost any other database. The effect is a cross join . Similarly, you can use an on clause with cross join , which also differs from standard SQL. A cross join creates a Cartesian product --

Multiple INNER JOIN SQL ACCESS

阅读更多关于 Multiple INNER JOIN SQL ACCESS

Syntax Error (missing Operator) in query expression 'tbl_employee.emp_id = tbl_netpay.emp_id INNER JOIN tbl_gross ON tbl_employee.emp_id = tbl_gross.emp_ID INNER JOIN tbl_tax ON tbl_employee.emp_id - tbl_tax.emp_ID'. SELECT tbl_employee.emp_ID, tbl_employee.emp_name, tbl_gross.BasicSalary, tbl_gross.totalOT, tbl_netpay.totalGross, tbl_tax.totalLate, tbl_tax.allowance, tbl_tax.SSS, tbl_tax.PhilHealth, tbl_tax.GSIS, tbl_tax.HDMF, tbl_netpay.totalDeduc, tbl_netpay.emp_ti, tbl_netpay.emp_wt, tbl_netpay.emp_np FROM tbl_employee INNER JOIN tbl_netpay ON tbl_employee.emp_id = tbl_netpay.emp_id INNER