"I have 3 Tables which is Admin table,Studentinfo Table and Useraccount Table.
i want to join that 3 tables for my search engine. :(
im beginner in sql anyone can help me?"
SELECT Username,Name,Position,Status,ImageName FROM useraccount
JOIN admin ON admin.username = useraccount.username
JOIN studentinfo ON studentinfo.username = useraccount.username
where Name Like '%Search%';
"That is my code but nothing happen."
When dealing with multiple tables you would have to compensate for column name ambiguity as the same column name could be available in other joining tables and there is no way for the query execution engine to know which one you want returned.
You can easily fix this by adding an alias or table name to referenced column Name
TableAlias.ColumnName
( or )
TableName.ColumnName
Example:
SELECT Col1
FROM table1
JOIN table2
ON table1.Col1= table2.Col2
Will generate a Ambiguous column name error.
SELECT t1.Col1
FROM table1 t1
JOIN table2 t2
ON t1.Col1= t2.Col2
Or
SELECT table1.Col1
FROM table1
JOIN table2
ON table1.Col1= table2.Col2
The changes:
Added the prefix "t1" or "TableName" to the requested column, so that the engine knows which table we want the data from
Added table aliases in the FROM / JOIN clauses to shorten the code
Scenario Example:
SELECT <TableName>.Username,
<TableName>.Name,
<TableName>.Position,
<TableName>.Status,
<TableName>.ImageName
FROM useraccount
JOIN admin
ON admin.username = useraccount.username
JOIN studentinfo
ON studentinfo.username = useraccount.username
WHERE <TableName>.Name LIKE '%Search%';
Related
I know that I can use the OR SQL operator on the same column of a table like the following:
SELECT * FROM users WHERE last_name = 'Peter' OR last_name = 'Smith';
But the situation I have right now is that I'm trying to use the OR operator on two different tables (different column names). Is that possible? How can I achieve that in an SQL query?
And yes there is a foreign key column that links one table to the primary key column of the other table.
Thanks in advance for any help.
If the fields in the different tables have the same name, you can distinguish them with tablename.fieldname, if the tables have the same name (in different schemas), you can further qualify the names with schemaname.tablename.fieldname.
Of course, all tables referenced in the WHERE and SELECT clauses should be included in the FROM clause.
Note: If a table is aliased in the FROM, the alias should be used instead of the table name.
You cannot display (or use in WHERE conditions, etc...) fields from a table that not included in the FROM; however, you can use subqueries on those tables.
Examples:
...
FROM table1 AS t1
WHERE t1.field1 = somevalue
OR EXISTS (
SELECT *
FROM table2 AS t2
WHERE t2.somefield = someothervalue
)
...
or
SELECT t1.field1
, (SELECT t2.somefield FROM table2 AS t2 WHERE t2.anotherfield = somevalue LIMIT 1) AS t2Val
FROM table1 AS t1
...
Yes , it is possible
SELECT users.* FROM users,countries WHERE users.last_name = 'Peter' OR countries.name = 'mexico' AND users.idCountry=countries.id;
I have three tables that I need to query in order to get my results.
Table 1 has an AppId and a ProjectID
Table2 has an AppID and an AppName.
Table 3 has a ProjectID and a ProjectName
I want to get out of this a list, By AppName, the ProjectNames they are tied to.
So far, a basic query to get what I want works, but I only get the ID's. I need to somehow join these to get the names associated. I need to somehow join this to table2 with the project name information, and table 2 with the appname information.
Select * from Table1 ( this table has only ID's, not names)
Order by AppId
You can join the tables like this:
Select t2.AppName, t3.ProjectName
from table1 t1
inner join table2 t2 on t2.AppID = t1.AppID
inner join table3 t3 on t3.ProjectID = t1.ProjectID
I want to create a table that needs to be a combination of selected columns from three or more tables. I don't have any sample data, just added the columns for explanation.
Table 1
A|B1|C1|D1|E1|F1|G1|H1|I1|J1
Table 2
A|B2|C2|D2|E2|F2|G2
Table 3
A|B3|C3|D3|E3|F3|G3
Resultant New table must have
A|B1|E1|F1|G1|J1|C2|D2|G2|B3|D3|F3
I'm not sure if I need to use a FULL JOIN or use UNIONS.
Each of these tables contain more than 400,000 rows. Any help here on what query needs to be included would be really helpful.
You can try the below query:
select t1.A,t1.B1,t3.E1,t1.F1,t1.G1,t1.J1,t2.C2,t2.D2,t2.G2,t3.B3,t3.D3,t3.F3
from table1 t1 join table2 t2 on t1.A = t2.A
join table3 t3 join table2 t2 on t3.A = t2.A
As Palec commented correctly in the other answer, so adding a bit of explanation to the answer.
You need to use the JOINS for this problem instead of UNION. The reason why I am saying to use JOINS over UNION is UNION combines the data/result of two or more queries into a single result set which includes all the rows which exist in the queries in your UNION. But when you are using JOINs, you can retrieve data from two or more tables based on logical relationships between the tables.
Also to add that you should add an alias name to your table so that it becomes easy to retrieve the column in the select query and also while linking the table.
Join is the correct way:
select table1.A,B1,E1,F1,G1,J1,C2,D2,G2,B3,D3,F3 from table1 join table2 on table1.A = table2.A
join table3 join table2 on table3.A = table2.A
I don't know why I am confused with this query.
I have two table: Table A with 900 records and Table B with 800 records. Both table need to contain the same data but there is some mismatch.
I need to write a mysql query to insert missing 100 records from Table A to Table B.
In the end, both Table A and Table B should be identical.
I do not want to truncate all the entries first and then do a insert from another table. So please any help is appreciated.
Thank you.
It is also possible to use LEFT OUTER JOIN for that. This will avoid subquery overhead (when system might execute subquery one time for each record of outer query) like in John Woo's answer, and will avoid doing unnecessary work overwriting already existing 800 records like in user2340435's one:
INSERT INTO b
SELECT a.* FROM a
LEFT OUTER JOIN b ON b.id = a.id
WHERE b.id IS NULL;
This will first select all rows from A and B tables including all columns from both tables, but for rows which exist in A and don't exist in B all columns for B table will be NULL.
Then it filter only such latter rows (WHERE b.id IS NULL),
and at last it inserts all these rows into B table.
I think you can use IN for this. (this is a simpliplification of your query)
INSERT INTO table2 (id, name)
SELECT id, name
FROM table1
WHERE (id,name) NOT IN
(SELECT id, name
FROM table2);
SQLFiddle Demo
AS you can see on the demonstration, table2 has only 1 records but after executing the query, 2 records were inserted on table2.
If it's mysql and the tables are identical, then this should work:
REPLACE INTO table1 SELECT * FROM table2;
This will insert the missing records into Table1
INSERT INTO Table2
(Col1, Col2....)
(
SELECT Col1, Col2,... FROM Table1
EXCEPT
SELECT Col1, Col2,... FROM Table2
)
You can then run an update query to match the records that differ.
UPDATE Table2
SET
Col1= T1.Col1,
Col2= T1.Col2,
FROM
Table T1
INNER JOIN
Table2 T2
ON
T1.Col1 = T2.Col1
Code also works when a group by and having clauses are used. Tested SQL 2012 (11.0.5058) Tab1 is source with new records, Tab 2 is the destination to be updated. Tab 2 also has an Identity column. (Yes folks, real world is not as neat and clean as the lab assignments)
INSERT INTO Tab2
SELECT a.T1,a.T2,a.T3,a.T4,a.Val1,a.Val2,a.Val3,a.Val4,-9,-9,-9,-9,MIN(hits) MinHit,MAX(hits) MaxHit,SUM(count) SumCnt, count(distinct(week)) WkCnt
FROM Tab1 a
LEFT OUTER JOIN Tab2 b ON b.t1 = a.t1 and b.t2 = a.t2 and b.t3 = a.t3 and b.t4 = a.t4 and b.val1 = a.val1 and b.val2 = a.val2 and b.val3 = a.val3 and b.val4 = a.val4
WHERE b.t1 IS NULL or b.Val1 is NULL
group by a.T1,a.T2,a.T3,a.T4,a.Val1,a.Val2,a.Val3,a.Val4 having MAX(returns)<4 and COUNT(distinct(week))>2 ;
Imagine I have table1 which has a column named 'table_name'. I use table1.table_name to store the name of another table in the database. The referenceable tables would all have a field 'target_id.
Is is possible to use table_name in a JOIN statement?
For example:
SELECT t1.*, t2.* FROM table1 AS t1
JOIN table1.table_name AS t2 ON t1.table1_id = t2.target_id
The obvious solution is to use the script (C++ in my case) to get the table name first, and construct a SQL query from it. The question is: can we bypass the script and do this directly in SQL (MySQL)?
Edit: What is dynamic SQL?
The only chance you have is to do 2 SQL statements:
select the tablename you need
use this table-name to dynamically build the secound query to get the data you need - what you want isn't possible to do with SQL directly (and it sounds like you've designed your database wrong in some way - but that's hard to say without knowing what's the goal of it).
I know I'm late to the party, but I wanted to offer a different solution. I see this sort of thing a lot in audit tables. The column table_name would refer to "what table was changed" and table1_id would refer to the ID of the row that changed in that table. In this case, the audit table is pointing back to many different tables that don't normally get joined.
Here goes:
SELECT t1.*, t2.*, t3.*, t4.*, t5.*
FROM table1 AS t1
left JOIN table2 AS t2
ON t1.table1_id = t2.target_id
and t1.table_name = 'table2'
left JOIN table3 AS t3
ON t1.table1_id = t3.target_id
and t1.table_name = 'table3'
left JOIN table4 AS t4
ON t1.table1_id = t4.target_id
and t1.table_name = 'table4'
left JOIN table5 AS t5
ON t1.table1_id = t5.target_id
and t1.table_name = 'table5'
Of course, the main drawback is that each table that can be possibly referenced needs to be explicitly included in the SQL command.
You can get more elegant output using this as your select list:
SELECT
t1.*,
coalesce(t2.fieldA, t3.fieldA, t4.fieldA, t5.fieldA) as fieldA,
coalesce(t2.fieldB, t3.fieldB, t4.fieldB, t5.fieldB) as fieldB
etc