Is the following valid in SQL (theoretical)?
UPDATE Classes
SET bore = bore * 2.5;
I can't find a source that says whether this is valid or not.
This should multiply every entry in the bore attribute by 2.5. If not, is there a way to multiply a column by a scalar and update?
The SQL is correct, see the SQL fiddle example on the link below. It creates the table, inserts some values and updates the table with your SQL.
See this SQL fiddle for example
It's valid and correct. You're assigning to each row of bore column a new value, multiplying the current value by 2.5. This is perfectly fine in the UPDATE statement.
The MySQL documentation has a similar example:
If you access a column from the table to be updated in an expression,
UPDATE uses the current value of the column. For example, the following statement sets col1 > to one more than its current value:
UPDATE t1 SET col1 = col1 + 1;
You can then suppose that this is valid.
Related
I've created a MySQL sproc which returns 3 separate result sets. I'm implementing the npm mysql package downstream to exec the sproc and get a result structured in json with the 3 result sets. I need the ability to filter the json result sets that are returned based on some type of indicator in each result set. For example, if I wanted to get the result set from the json response which deals specifically with Suppliers then I could use some type of js filter similar to this:
var supplierResultSet = mySqlJsonResults.filter(x => x.ResultType === 'SupplierResults');
I think SQL Server provides the ability to include a hard-coded column value in a SQL result set like this:
select
'SupplierResults',
*
from
supplier
However, this approach appears to be invalid in MySQL b/c MySQL Workbench is telling me that the sproc syntax is invalid and won't let me save the changes. Do you know if something like what I'm trying to achieve is possible in MySQL and if not then can you recommend alternative approaches that would help me achieve my ultimate goal of including some type of fixed indicator in each result set to provide a handle for downstream filtering of the json response?
If I followed you correctly, you just need to prefix * with the table name or alias:
select 'SupplierResults' hardcoded, s.* from supplier s
As far as I know, this is the SQL Standard. select * is valid only when no other expression is added in the selec clause; SQL Server is lax about this, but most other databases follow the standard.
It is also a good idea to assign a name to the column that contains the hardcoded value (I named it hardcoded in the above query).
In MySQL you can simply put the * first:
SELECT *, 'SupplierResults'
FROM supplier
Demo on dbfiddle
To be more specific, in your case, in your query you would need to do this
select
'SupplierResults',
supplier.* -- <-- this
from
supplier
Try this
create table a (f1 int);
insert into a values (1);
select 'xxx', f1, a.* from a;
Basically, if there are other fields in select, prefix '*' with table name or alias
I would like to get the number of row affected / deleted / updated with a TMSSqlRow.
Here is how the job is:
the file use contains a lot of sql statement like DELETE ... INSERT ... UPDATE...
each row are separate by ";"
But now, I would like to get result of each statement (x rows updated, like results are display in management studio).
When I go to "advanced settings" tab of tmssqlrow, I select " Propagate QUERY's recordset" and select a column I created before (Object Type).
On execution, I have this error:
The executeQuery method must return a result set.
So, how I can get the result of each statement and insert it (by example) in a database / file?
The option "Propagate QUERY's recordset" must be used in combination with a tParseRecordSet in order to extract info from the returned recordset. However, that is not sufficent: you must explicitly write the query to return the number of records updated/deleted.
Here's what I did:
My tJDBCRow (same as tMSSqlRow) query looks like this (notice how I had to add 'set nocount on' before the update query, and 'select ##rowcount' after)
tParseRecordSet retrieves the number of lines from the column resultset (nbLines is the alias of my rowcount)
If you need the number of rows affected, a better option is to use the tMSSqlOutput component which can update,insert or delete rows. After execution, the component provides global variables to show how many rows were affected by the operation.
((Integer)globalMap.get("tMSSqlOutput_1_NB_LINE"))
((Integer)globalMap.get("tMSSqlOutput_1_NB_LINE_UPDATED"))
((Integer)globalMap.get("tMSSqlOutput_1_NB_LINE_INSERTED"))
((Integer)globalMap.get("tMSSqlOutput_1_NB_LINE_DELETED"))
I'm working of generating sql request by parsing Excel-like formulas.
So for a given formula, I get this request :
SELECT IF(COL1='Y', SUM(EXPR),NULL)
FROM Table
I don't get the results I want. If I manually rewrite the request like this it works :
SELECT SUM(IF(COL1='Y', EXPR, NULL))
FROM Table
Also, the first request produces the right value if I add a GROUP BY statement, for COL1='Y' row :
SELECT IF(COL1='Y', SUM(EXPR),NULL)
FROM Table
GROUP BY COL1
Is there a way to keep the first syntax IF(COND, SUM(EXPR), NULL) and slightly edit it to make it works without a GROUP BY statement ?
You have to use GROUP BY since you are using SUM - otherwise SQL engine is not able to tell how do you want to summarize the column.
Alternatively you could summarize this column only:
SELECT SUM(EXPR)
FROM Table
WHERE COL1='Y'
But then you would have to run separate query for each such column, read: not recommended for performance reasons.
I was running through some of our code at work and came across this structure for an sql query and was sure it was a typo in the variables of our PHP, I ran it and it works.
Select column from table where value = column;
Anyone I know was always taught the correct syntax is:
Select column from table where column = value;
Is there any reason for this being legal, other than SQL just checks are both sides of an equation equal to each other?
I'm more posting this because I found it really interesting, like a 'the more you know' kind of thing.
The equality operator (=) is symmetric - if a=b is true, then so is b=a. a and b can be column names, values or complex expressions. It's common to use the form column=value, but syntactically speaking, it's completely equivalent to value=column.
Yes, you have it right sql just checks both sides of an equation. The equation could even contain a column on neither side! such as
SELECT column from table where 1=2;
The syntax of an SQL query is :
SELECT what_to_select
FROM which_table
WHERE conditions_to_satisfy;
You can use any condition you want, for example :
SELECT * FROM table WHERE 1
will return you all the rows
while
SELECT * FROM table WHERE 0
will return you nothing
after a WHERE you must have a condition, nothing else
I want to update a mysql row, but I do not want to specify all the column names.
The table has 9 rows and I always want to update the last 7 rows in the right order.
These are the Fields
id
projectid
fangate
home
thanks
overview
winner
modules.wallPost
modules.overviewParticipant
Is there any way I can update the last few records without specifying their names?
With an INSERT statement this can be done pretty easily by doing this:
INSERT INTO `settings`
VALUES (NULL, ...field values...)
So I was hoping I could do something like this:
UPDATE `settings`
VALUES (NULL, ...field values...)
WHERE ...statement...
But unfortunately that doesn't work.
If the two first columns make up the primary key (or a unique index) you could use replace
So basically instead of writing
UPDATE settings
SET fangate = $fangate,
home = $home,
thanks = $thanks
overview = $overview,
winner = $winner,
modules.wallPost = $modules.wallPost,
modules.overviewParticipant = $modules.overviewParticipant
WHERE id = $id AND procjectId = $projectId
You will write
REPLACE INTO settings
VALUES ($id,
$projectId,
$fangate,
$home,
$thanks
$overview,
$winner,
$modules.wallPost,
$modules.overviewParticipant)
Of course this only works if the row already exist, otherwise it will be created. Also, it will cause a DELETE and an INSERT behind the scene, if that matters.
You can't. You always have to specify the column names, because UPDATE doesn't edit a whole row, it edits specified columns.
Here's a link with the UPDATE syntax:
http://dev.mysql.com/doc/refman/5.0/en/update.html
No, it works on the INSERT because even if you didn't specify the column name but you have supplied all values in the VALUE clause. Now, in UPDATE, you need to specify which column name will the value be associated.
UPDATE syntax requires the column names that will be modified.
Are you always updating the same table and columns?
In that case one way would be to define a stored procedure in your schema.
That way you could just do:
CALL update_settings(id, projectid, values_of_last_7 ..);
Although you would have to create the procedure, check the Mysql web pages for how to do this, eg:
http://docs.oracle.com/cd/E17952_01/refman-5.0-en/create-procedure.html
I'm afraid you can't afford not specifying the column names.
You can refer to the update documentation here.