Is there any way to do something like :
SELECT * FROM TABLE WHERE COLUMN_NUMBER = 1;
?
No, you can't. Column order doesn't really matter in MySQL. See the below question for more details.
mysql - selecting values from a table given column number
If your table has a column named COLUMN_NUMBER and you want to retrieve rows from the table where that column contains a value of '1', that query should do the trick.
I suspect that what you are trying to do is reference an expression in the select list with an alias. And that is not supported. An expression in the WHERE clause that references a column must reference the column by name.
We can play some tricks with inline views, to give an alias to an expression, but this is not efficient in terms of WHERE predicates, because of the way MySQL materializes a derived table. And, in that case, its a name given to the column in the inline view that has to be referenced in the outer query.
How I did it:
I'm trying to take (last 3 values of) column number 4 in sometable.
set #mydb=(SELECT DATABASE());
set #mycol=(select COLUMN_NAME from information_schema.columns where
table_schema=#mydb and table_name='sometable' and ordinal_position = 4);
SELECT Date,#mycol FROM sometable ORDER BY Date DESC LIMIT 3;
Of course, if Database name is known, first line could by whiped and #mydb replaced by real database name.
You can do this trick
Example:
$query="select * from employee";
$result=mysql_query($query);
$meta=mysql_fetch_field($result,0) // 0 is first field in table , 1 is second one ,,, etc
$theNameofFirstField=$meta->name; // this well return first field name in table
// now you can use it in other query
$seconQuery="select $theNameofFirstField from employee";
Related
I have tried to select something with SQL, and I've a problem with it.
What I want:
SQL SELECT * FROM table WHERE ? = '5';
Select everything which = 5, BUT not specify from which column.
Example:
From this ""database"", you should receive the 1st and the last row.
Is that possible?
You have to list the columns but you can use in. The where clause looks like:
where 5 in (price, height)
Note: This assumes that the columns have the same type. You could get type conversion errors if they are not.
Also, given the names of the column and the data, I assume that the columns are stored as numbers. Hence, I dropped the single quotes around 5. If they are really strings, then use the single quotes.
you need to add a condition to your query with or keyword so if any of them match the row will be shown as a result
SELECT * FROM tablename WHERE price =5 or height= 5
better you list your columns by name instead of using * after SELECT
Is there a way to retrieve the column names of a query that returns no data?
The result of this query would be empty.
Is there a way how to find the column names when there's no result?
Please note that I'm aware of solutions using DESCRIBE and select column_name from information_schema.columns where table_name='person';
but I need a more flexible solution that will fit these multicolumn queries.
Please also note that I am still using the original PHP MySQL extention (so no MySQLi, and no PDO).
If you wrap your query with the following SQL, it will always return the column names from your query, even if it is an empty query result:
select myQuery.*
from (select 1) as ignoreMe
left join (
select * from myTable where false -- insert your query here
) as myQuery on true
Note: When the results of the subquery are empty, a single row of null values will be returned. If there is data in the subquery it won't affect the output because it creates a cross-product with a single row...and value x 1 = value
Execute following command if the result of your previous query is empty
SHOW columns FROM your-table;
For more details check this.
I'm not sure if it will satisfy you but you can do this
SELECT *, COUNT(*) FROM table;
It will return null values (except last column which you can ignore) if the query is empty and you will be able to access all columns. It's not proper way of doing it and selecting names from INFORMATION_SCHEMA would be much better solution.
Please note that result is aggregated and you need to use GROUP BY to get more results if there are any.
You should ,
Select COLUMN_NAME From INFORMATION_SCHEMA.COLUMNS
Where TABLE_SCHEMA='yourdb'
AND TABLE_NAME='yourtablename';
I'm trying to run a SQL SELECT statement against a column that is of type SET. The table is called myTable and the columns in myTable are called base_props and names. The base_props column is of type SET. The values in base_prop are vb,nt, cnt,poss and loc. So I would like to SELECT entries from the column 'name' where base_props have both the values, vb and poss. The results I'm looking to get may have values other than just vb and poss. So to be clear I would like to select all entries that have the values vb and poss regardless if they have other values as well. I've tried the following SQL queries but I can't get the desired results.
SELECT name from myTable WHERE base_props = 'vb' AND base_props = 'poss'
That query returns an empty result set. I've tried using FIND_IN_SET() and IN() but I couldn't get anywhere with that. I've written SQL statements before but never had to deal with columns that are type SET. Any help is appreciated.
The only thing I can come up with is using the LIKE keyword:
SELECT name FROM myTable WHERE (base_props LIKE '%vb%' AND base_props LIKE '%poss%');
This will make sure both vb and cnt are in the base_props column. Of course you can use cnt, nt and loc in there, or any number of base_props values in the sql, just add more AND statements.
OR as a deleted answer by samitha pointed out, you can use FIND_IN_SET:
SELECT name from myTable WHERE FIND_IN_SET('vb', base_props) AND FIND_IN_SET('poss', base_props);
Comment (by spencer7593): "both of these work, but there is a slight difference. The LIKE operator will actually match any member that includes the search string anywhere in a term; the FIND_IN_SET function will only match an exact member. It's also possible to search for members in set by the order they appear in the SET definition, using the MySQL BITAND operator: for example, to match the 1st and 4th members of the set: WHERE base_props & 1 AND base_props & 8". So for example, if you have 'a' and 'aaa' in your set, then using the LIKE "%a%" method will also return rows containing 'aaa'.
Conclusion: use the FIND_IN_SET solution since it will work for all cases.
FIND_IN_SET return index, Try this
SELECT name from myTable WHERE FIND_IN_SET(base_props, 'vb') > 0 AND
FIND_IN_SET(base_props, 'poss') > 0
What I'm Using: The most recent MySQL on Ubuntu 12.
The Set Up: Suppose I have a table "EmployeePayment" with "Name" and "Hours" for each employee. Suppose I already have it populated with values.
The Question: When I use the command
select * from EmployeePayment where Name in ('');
I get the empty set, as I'd expect. But, when I use
select * from EmployeePayment where Name in ('' or '');
I get the entire table returned. Moreover, if I'm picky and put in the command
select Name, SUM(Hours) from EmployeePayment where Name in ('' or '');
then it only returns whatever is the top name from the table. What's happening with this "in" command?
First off, you need to get rid of the or, the proper syntax for the in clause uses commas to separate the possibilities, such as:
sql> select name from people where status in ('intelligent', 'good looking')
pax
1 row returned
What your current variant is doing is applying the or operator to give you a one-element in-list. See here for more detail.
The reason why you're only getting one row for the aggregated query is because you have no group by clause, so you're grouping all rows. Most DBMS' would then complain about having a non-aggregated column that isn't part of the grouping, but MySQL is a bit fancy-free and footloose with the rules in that regard.
It's obviously grouping over the whole table (as it should) but applying some default aggregating function to the name (which it probably shouldn't, but does according to its documentation).
This MySQL extension is covered here but heed the warning: MySQL can choose any of the myriad possible values for these non-aggregated, non-group-by columns, so it's more useful when you know that all the rows in a given group share the same value for the column.
You're effectively doing this:
select * from EmployeePayment where Name in (0);
The OR expression evaluates to 0, and WHERE Name IN (0); returns all rows. You have to use the proper IN syntax as suggested in the other answers:
SELECT * FROM EmployeePayment WHERE Name IN ('foo', 'bar');
IN uses comma separated values, for example: WHERE Name IN ('tim','beth')
So try WHERE Name IN ('','');
But more importantly, why would you want to check where a value is empty or empty? Or was that just to get the question across?
http://dev.mysql.com/doc/refman/5.0/en/comparison-operators.html#function_in
I am trying to query a table in mysql based on the length of a string in a specific column. I know mysql has a function called LENGTH(), but that returns the length of the string. I want to be able to pull data based on the result of the LENGTH() function.
Example:
SELECT * table WHERE LENGTH(word) = 6
of course that does not work. I read through http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function%5Flength but could not find anything to help me.
yes I could make something in PhP to accomplish this, but I would like to do it at the query level.
Any help?
Try:
SELECT *
FROM table
WHERE LENGTH(RTRIM(word)) = 6
I believe you wanted to use query SELECT * FROM tableName WHERE LENGTH(word) = 6; (assuming that the word is name of column in tableName).
This is very unfortunate solution on large tables, you should create new column and use UPDATE tableName SET wordLength = LENGTH( word).