I'd like to update the value of column A by applying a function to column B.
Is there a simple solution of the form:
knex('table')
.update({
colA: func(${colB})
})
Yes, there is a way to do this within Knex.
For SQL functions which don’t have explicit support in Knex you use knex.raw(SQLstring, parmArray) to encapsulate a SQL snippet or knex.schema.raw(...) to produce an entire SQL statement. And you use single question marks ? for value replacements, and double question marks ?? for field identifier replacements. (see link)
So the SQL: UPDATE table SET colA = func(colB)
... can be produced by including a SQL snippet: (you were close)
knex('table')
.update({
colA: knex.raw( 'func(??)', ['colB'] )
})
... or as full raw SQL:
knex.schema.raw( 'UPDATE table SET ?? = func(??)', ['colA', 'colB'] )
Cheers, Gary.
Related
I'm new to node-postgres and trying to pass in parameters connected to a table alias, but it's not working. How can I parameterize the simple query below? Take something like
const pgQuery = 'SELECT t1.YEAR as year, t1.CODE as code FROM data t1;';
and instead do something like
const pgQuery = 'SELECT t1.$1 as year, t1.$2 as code FROM data t1;';
const values = ['YEAR', 'CODE'];
Per the docs here:
https://node-postgres.com/features/queries
PostgreSQL does not support parameters for identifiers. If you need to have dynamic database, schema, table, or column names (e.g. in DDL statements) use pg-format package for handling escaping these values to ensure you do not have SQL injection!
Which takes you here:
https://www.npmjs.com/package/pg-format
Repo:
https://github.com/datalanche/node-pg-format
I would like to know how can I store the value of subquery to use it in an operation after it recieve the value. For example:
Select IDTruck
, TruckPrice = (select "TruckPrice" from "Table1" where ("TruckID" = '123'))
, TruckUnit = (select "TruckUnit" from "Table2" )
, TruckPrice * TruckUnit as "PriceTotal"
from Table3
I just want to store the value and then use it in the operation so I don't have to do the select again.
I'm not sure why it should be necessary to store the values in variables for usage in your case. I think the calculation can be done also by joining just the data (assuming that table3 contains a reference to table1 and table2).
Your example above would also not work, because TruckPrice and TruckUnits are no atomar results.
So please try to refactor your statement to use joins.
I have a query (Update statement) wrapped in a function and will need to perform the same statement on multiple columns during the course of my script
async function update_percentage_value(value, id){
(async () => {
const client = await pool.connect();
try {
const res = await client.query('UPDATE fixtures SET column_1_percentage = ($1) WHERE id = ($2) RETURNING *', [value, id]);
} finally {
client.release();
}
})().catch(e => console.log(e.stack))
}
I then call this function
update_percentage_value(50, 2);
I have many columns to update at various points of my script, each one needs to be done at the time. I would like to be able to just call the one function, passing the column name, value and id.
My table looks like below
CREATE TABLE fixtures (
ID SERIAL PRIMARY KEY,
home_team VARCHAR,
away_team VARCHAR,
column_1_percentage INTEGER,
column_2_percentage INTEGER,
column_3_percentage INTEGER,
column_4_percentage INTEGER
);
Is it at all possible to do this?
I'm going to post the solution that was advised by Sehrope Sarkuni via the node-postgres GitHub repo. This helped me a lot and works for what I require:
No column names are identifiers and they can't be specified as parameters. They have to be included in the text of the SQL command.
It is possible but you have to build the SQL text with the column names. If you're going to dynamically build SQL you should make sure to escape the components using something like pg-format or use an ORM that handles this type of thing.
So something like:
const format = require('pg-format');
async function updateFixtures(id, column, value) {
const sql = format('UPDATE fixtures SET %I = $1 WHERE id = $2', column);
await pool.query(sql, [value, id]);
}
Also if you're doing multiple updates to the same row back-to-back then you're likely better off with a single UPDATE statement that modifies all the columns rather than separate statements as they'd be both slower and generate more WAL on the server.
To get the column names of the table, you can query the information_schema.columns table which stores the details of column structure of your table, this would help you in framing a dynamic query for updating a specific column based on a specific result.
You can get the column names of the table with the help of following query:
select column_name from information_schema.columns where table_name='fixtures' and table_schema='public';
The above query would give you the list of columns in the table.
Now to update each one for a specific purpose, You can store the result set of column name to a variable and pass that variable to the function to perform the required action.
I have an Object that maps column names to values. The columns to be updated are not known beforehand and are decided at run-time.
e.g. map = {col1: "value1", col2: "value2"}.
I want to execute an UPDATE query, updating a table with those columns to the corresponding values. Can I do the following? If not, is there an elegant way of doing it without building the query manually?
db.none('UPDATE mytable SET $1 WHERE id = 99', map)
is there an elegant way of doing it without building the query manually?
Yes, there is, by using the helpers for SQL generation.
You can pre-declare a static object like this:
const cs = new pgp.helpers.ColumnSet(['col1', 'col2'], {table: 'mytable'});
And then use it like this, via helpers.update:
const sql = pgp.helpers.update(data, cs) + /* WHERE clause with the condition */;
// and then execute it:
db.none(sql).then(data => {}).catch(error => {})
This approach will work with both a single object and an array of objects, and you will just append the update condition accordingly.
See also: PostgreSQL multi-row updates in Node.js
What if the column names are not known beforehand?
For that see: Dynamic named parameters in pg-promise, and note that a proper answer would depend on how you intend to cast types of such columns.
Something like this :
map = {col1: "value1", col2: "value2",id:"existingId"}.
db.none("UPDATE mytable SET col1=${col1}, col2=${col2} where id=${id}", map)
I want to perform a simple join on two tables (BusinessUnit and UserBusinessUnit), so I can get a list of all BusinessUnits allocated to a given user.
The first attempt works, but there's no override of Select which allows me to restrict the columns returned (I get all columns from both tables):
var db = new KensDB();
SqlQuery query = db.Select
.From<BusinessUnit>()
.InnerJoin<UserBusinessUnit>( BusinessUnitTable.IdColumn, UserBusinessUnitTable.BusinessUnitIdColumn )
.Where( BusinessUnitTable.RecordStatusColumn ).IsEqualTo( 1 )
.And( UserBusinessUnitTable.UserIdColumn ).IsEqualTo( userId );
The second attept allows the column name restriction, but the generated sql contains pluralised table names (?)
SqlQuery query = new Select( new string[] { BusinessUnitTable.IdColumn, BusinessUnitTable.NameColumn } )
.From<BusinessUnit>()
.InnerJoin<UserBusinessUnit>( BusinessUnitTable.IdColumn, UserBusinessUnitTable.BusinessUnitIdColumn )
.Where( BusinessUnitTable.RecordStatusColumn ).IsEqualTo( 1 )
.And( UserBusinessUnitTable.UserIdColumn ).IsEqualTo( userId );
Produces...
SELECT [BusinessUnits].[Id], [BusinessUnits].[Name]
FROM [BusinessUnits]
INNER JOIN [UserBusinessUnits]
ON [BusinessUnits].[Id] = [UserBusinessUnits].[BusinessUnitId]
WHERE [BusinessUnits].[RecordStatus] = #0
AND [UserBusinessUnits].[UserId] = #1
So, two questions:
- How do I restrict the columns returned in method 1?
- Why does method 2 pluralise the column names in the generated SQL (and can I get round this?)
I'm using 3.0.0.3...
So far my experience with 3.0.0.3 suggests that this is not possible yet with the query tool, although it is with version 2.
I think the preferred method (so far) with version 3 is to use a linq query with something like:
var busUnits = from b in BusinessUnit.All()
join u in UserBusinessUnit.All() on b.Id equals u.BusinessUnitId
select b;
I ran into the pluralized table names myself, but it was because I'd only re-run one template after making schema changes.
Once I re-ran all the templates, the plural table names went away.
Try re-running all 4 templates and see if that solves it for you.