Heyy I'm new to sql and I'd just like to know if there's a way to retrieve select statements with conditions from other tables.
I want to select all name values that have a number that identifies that they have committed a crime. I only want to select a name once.
"SELECT distinct * FROM Table1 WHERE number LIKE table2.number "
Are you looking for IN?
SELECT t1.*
FROM Table1 t1
WHERE t1.number IN (SELECT t2.number FROM table2 t2 t2.number);
Under most circumstances, the rows in a table should be unique. So, you don't need SELECT DISTINCT. The DISTINCT can add a considerable amount of overhead to such a query.
You can able to use INNER JOIN like below,
select tbl1.Name from tableOne tbl1
inner join tableTwo tbl2 ON tbl1.commonKey = tbl2.commonKey
where tbl1.columnName = 'any value'
Related
I want to join two tables in Access based on different wildcards for different rows.
The first, table1, contains rows with different wildcards and table2 contains the column that should be matched with the wildcards in table1.
I imagine the SQL code to look like:
SELECT *
FROM table2
LEFT JOIN table1
ON table2.subject LIKE table1.wildcard
The tables look like this: https://imgur.com/a/O9OPAL6
The third pictures shows the result that I want.
How do I execute the join or is there an alternative?
I don't think MySQL support non-equality conditions for JOINs. So, you can do this as:
SELECT * -- first get the matches
FROM table2 as t2, -- ugg, why doesn't it support CROSS JOIN
table1 as t1
WHERE t2.subject LIKE t1.wildcard
UNION ALL
SELECT * -- then get the non-matches
FROM table2 as t2 LEFT JOIN
table1 as t1
ON 1 = 0 -- always false but gets the same columns
WHERE NOT EXISTS (SELECT 1
FROM table1 as t1
WHERE t2.subject LIKE t1.wildcard
);
I have two tables where each one contains columns with numbers. I need to compare columns in both tables and extract the number that does exist in first table, and does not exist in second one. I don't need unique value.
I wrote this query:
SELECT Table1.Numbers, Table1.Name
FROM Table1, Table2
WHERE Table1.Numbers != Table2.numbers
Since I am working on several million records can someone recommend more efficient query which would provide me with identical results?
I would use NOT EXISTS:
SELECT Table1.Numbers, Table1.Name
FROM Table1
WHERE NOT EXISTS(
SELECT 1 FROM Table2
WHERE Table1.Numbers=Table2.Numbers
)
Other approaches:
Should I use NOT IN, OUTER APPLY, LEFT OUTER JOIN, EXCEPT, or NOT EXISTS?
You can do this easily by checking for the existance on the number in Table2.
SELECT T1.Numbers
,T1.Name
FROM Table1 T1
WHERE NOT EXISTS (SELECT 1 FROM Table2 T2 WHERE T2.Numbers = T1.Numbers)
Try this (assuming that your Numbers column are not nullable)
SELECT T1.Numbers, T1.Name
FROM Table1 AS T1
LEFT JOIN Table2 AS T2 ON T1.Numbers = T2.Numbers
WHERE T2.Numbers IS NULL;
SELECT
Table1.Numbers, Table1.Name
FROM
Table1, Table2
GROUP BY
Table1, Table2
HAVING
COUNT(*) > 1
In postgresql I can use subquery in join condition
SELECT *
FROM table1 LEFT JOIN table2
ON table1.id1 = (SELECT id2 FROM table2 LIMIT 1);
But when I try to use it in Access
SELECT *
FROM table1 LEFT JOIN table2
ON table1.id1 = (SELECT TOP 1 id2 FROM table2);
I get syntax error. Is it actually impossible in Access or just my mistake?
I know that I can get the same result with WHERE, but my question is about possibilities of JOIN in Access.
It's not possible, per the MSDN documentation:
Syntax
FROM table1 [ LEFT | RIGHT ] JOIN table2 ON table1.field1 compopr table2.field2
And (emphasis mine):
field1, field2: The names of the fields that are joined. The fields must be of the same data type and contain the same kind of data, but they do not need to have the same name.
It appears you can't even have hard-coded values in your join; you must specify the column name to join against.
In your case, you would want:
SELECT *
FROM Table1
LEFT JOIN (
SELECT DISTINCT TOP 1 ID
FROM Table2
ORDER BY ID
) Table2Derived ON Table1.ID = Table2Derived.ID
Q: If I have two tables joined together, and I want to get (*) from the first table, I mean all the fields of the first table.
Shall I write all the fields names of the first table in the query? Or is there some way to select * just from the first table.
You should not to list all the fields, see the example:
SELECT DISTINCT t1.*
from T1
join t2 on condition
first_table.* should do the trick.
Sounds more like a semi join. Consider rewriting e.g.
SELECT DISTINCT T1.*
FROM T1 JOIN T2 ON T1.id = T2.id;
can be re-written as
SELECT *
FROM T1
WHERE id IN (SELECT id FROM T2);
I am a little confused as to how to approach this SQL query.
I have two tables (equal number of records), and I would like to return a column with which is the division between the two.
In other words, here is my not-working-correctly query:
SELECT( (SELECT v FROM Table1) / (SELECT DotProduct FROM Table2) );
How would I do this? All I want it a column where each row equals the same row in Table1 divided by the same row in Table2. The resulting table should have the same number of rows, but I am getting something with a lot more rows than the original two tables.
I am at a complete loss. Any advice?
It sounds like you have some kind of key between the two tables. You need an Inner Join:
select t1.v / t2.DotProduct
from Table1 as t1
inner join Table2 as t2
on t1.ForeignKey = t2.PrimaryKey
Should work. Just make sure you watch out for division by zero errors.
You didn't specify the full table structure so I will assume a common ID column to link rows in the tables.
SELECT table1.v/table2.DotProduct
FROM Table1 INNER JOIN Table2
ON (Table1.ID=Table2.ID)
You need to do a JOIN on the tables and divide the columns you want.
SELECT (Table1.v / Table2.DotProduct) FROM Table1 JOIN Table2 ON something
You need to substitue something to tell SQL how to match up the rows:
Something like: Table1.id = Table2.id
In case your fileds are both integers you need to do this to avoid integer math:
select t1.v / (t2.DotProduct*1.00)
from Table1 as t1
inner join Table2 as t2
on t1.ForeignKey = t2.PrimaryKey
If you have multiple values in table2 relating to values in table1 you need to specify which to use -here I chose the largest one.
select t1.v / (max(t2.DotProduct)*1.00)
from Table1 as t1
inner join Table2 as t2
on t1.ForeignKey = t2.PrimaryKey
Group By t1.v