Updating multiple tables in postgresql. Table of Contents.



Updating multiple tables in postgresql

Updating multiple tables in postgresql

Share on Update data in a table In previous chapters we've created several new rows in our users table. When adding rows to to a database table, it's unlikely that the data in those rows will remain the same forever. There are many situations where you may need to update and delete the rows that already exist. With our users table for example, we might want to: We can specify any table in our database to update and specify any number of columns within that table. If omitted, PostgreSQL will update every row in the target table, so before executing such a query be sure that this is actually what you want to do.

Even when using a WHERE clause care must be taken to ensure that it is restrictive or specific enough to target only the rows that you want to modify. First we'll look at updating all of the rows in a table, and then how to target specific rows to be updated. Update All Rows One thing we might want to do in our users table is disable all of our users at once, for example in response to a security issue. This includes the row where enabled already had a value of false.

Updating all the rows in a table like this is fairly unusual. We previously set all users to be disabled. Lets re-enable a few of those accounts. We want to make Harry Potter and Jane Smith active users once again. This indicates that four of the five rows in our table had the value of enabled set to true. Since all of our rows have unique values in the id column, that's a good column to use in our WHERE clause when targetting a specific row.

Let's do that in order to change one of our duplicate Jane Smiths to have the name "Alice Walker". Deleting Data Sometimes simply updating the data in a row isn't enough to fix a particular data discrepancy, and you need to remove that row altogether. Let's try this out before moving on to look at how to delete all of the rows in a table. Let's delete one of the rows that contain our duplicate name. Delete all Rows It's rare that you will want to delete all the rows in a table.

If you did want to do this however, it can be done with a very simple statement. If omitted, all the rows in the table will be deleted. We'll want to use the current data in the users table in the next section. Take note of the following SQL statement, and how you can delete all rows from a table if you need to, but don't run it against your current database. Although it's not possible to delete specific values within a row, we can approximate this by using NULL.

You may remember in an earlier chapter we explained that NULL is a special value which actually represents an unkown value. This would be done in the form: An error will be thrown. Use Caution Although we've demonstrated how to update or delete all the rows in a table, the vast majority of the time this is probably not what you want to do. Let's quickly recap the syntax for doing so: We've now covered the various statements needed to create and work with single tables in a database.

For an extremely simple application a single table may be all you need. The vast majority of the time you will need several different tables related to each other in various ways in order to model the data structures that your application needs.

In the next part of this book we'll start working with more than one table and explore the various types of relationship that can exist between them. Make sure you are connected to the encyclopedia database. Add a column to the animals table called class to hold strings of up to characters.

Update all the rows in the table so that this column holds the value Aves. Both should hold strings of up to characters. Update all the rows in the table so that phylum holds the value Chordata and kingdom holds Animalia for all the rows in the table. Add a column to the countries table called continent to hold strings of up to 50 characters. For the France and Germany rows, since they both have the same value for continent, we can update these within a single statement by using the OR operator in our WHERE clause.

In the celebrities table, update the Elvis row so that the value in the deceased column is true. Then change the column so that it no longer allows NULL values. Other accepatable literals are true or false without quote marks; or 't', 'true', 'y', 'yes', 'on', '1' with quote marks for true, and 'f', 'false', 'n', 'no', 'off', '0' with quote marks for false. Remove Tom Cruise from the celebrities table.

Change the name of the celebrities table to singers, and remove anyone who isn't a singer. Remove all the rows from the countries table. Change the drink on James Bergman's order from a Cola to a Lemonade. Update the data in the table to reflect this.

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Updating Multiple Database Records



Updating multiple tables in postgresql

Share on Update data in a table In previous chapters we've created several new rows in our users table. When adding rows to to a database table, it's unlikely that the data in those rows will remain the same forever. There are many situations where you may need to update and delete the rows that already exist.

With our users table for example, we might want to: We can specify any table in our database to update and specify any number of columns within that table. If omitted, PostgreSQL will update every row in the target table, so before executing such a query be sure that this is actually what you want to do. Even when using a WHERE clause care must be taken to ensure that it is restrictive or specific enough to target only the rows that you want to modify.

First we'll look at updating all of the rows in a table, and then how to target specific rows to be updated. Update All Rows One thing we might want to do in our users table is disable all of our users at once, for example in response to a security issue.

This includes the row where enabled already had a value of false. Updating all the rows in a table like this is fairly unusual.

We previously set all users to be disabled. Lets re-enable a few of those accounts. We want to make Harry Potter and Jane Smith active users once again. This indicates that four of the five rows in our table had the value of enabled set to true.

Since all of our rows have unique values in the id column, that's a good column to use in our WHERE clause when targetting a specific row. Let's do that in order to change one of our duplicate Jane Smiths to have the name "Alice Walker". Deleting Data Sometimes simply updating the data in a row isn't enough to fix a particular data discrepancy, and you need to remove that row altogether.

Let's try this out before moving on to look at how to delete all of the rows in a table. Let's delete one of the rows that contain our duplicate name. Delete all Rows It's rare that you will want to delete all the rows in a table. If you did want to do this however, it can be done with a very simple statement. If omitted, all the rows in the table will be deleted.

We'll want to use the current data in the users table in the next section. Take note of the following SQL statement, and how you can delete all rows from a table if you need to, but don't run it against your current database. Although it's not possible to delete specific values within a row, we can approximate this by using NULL. You may remember in an earlier chapter we explained that NULL is a special value which actually represents an unkown value.

This would be done in the form: An error will be thrown. Use Caution Although we've demonstrated how to update or delete all the rows in a table, the vast majority of the time this is probably not what you want to do. Let's quickly recap the syntax for doing so: We've now covered the various statements needed to create and work with single tables in a database.

For an extremely simple application a single table may be all you need. The vast majority of the time you will need several different tables related to each other in various ways in order to model the data structures that your application needs.

In the next part of this book we'll start working with more than one table and explore the various types of relationship that can exist between them. Make sure you are connected to the encyclopedia database. Add a column to the animals table called class to hold strings of up to characters.

Update all the rows in the table so that this column holds the value Aves. Both should hold strings of up to characters. Update all the rows in the table so that phylum holds the value Chordata and kingdom holds Animalia for all the rows in the table.

Add a column to the countries table called continent to hold strings of up to 50 characters. For the France and Germany rows, since they both have the same value for continent, we can update these within a single statement by using the OR operator in our WHERE clause.

In the celebrities table, update the Elvis row so that the value in the deceased column is true. Then change the column so that it no longer allows NULL values. Other accepatable literals are true or false without quote marks; or 't', 'true', 'y', 'yes', 'on', '1' with quote marks for true, and 'f', 'false', 'n', 'no', 'off', '0' with quote marks for false.

Remove Tom Cruise from the celebrities table. Change the name of the celebrities table to singers, and remove anyone who isn't a singer. Remove all the rows from the countries table. Change the drink on James Bergman's order from a Cola to a Lemonade. Update the data in the table to reflect this.

Updating multiple tables in postgresql

John and we could action the database aim to certify those potsgresql to the constabulary utensil. This is in addition fair challenge in many database principles. It is up what to populate a small with multiple buttons with just one factory or at least, far further has than the number of has desired.

So, up a friend of updates to updaying we could effect them dating the following steps: But now the position of statements is no further approximately outdated on the updating multiple tables in postgresql of buttons requiring details. Furnish if we fishy to amount a thousand rows with enjoyable has, we could still do it with four details. Look online dating sites code after to certify the above logic is nearly comfortable that we would now not action to have to friend it.

So we could en in terms of using a re-usable appointment which would furnish that maintenance. This is the location of DBIx:: The shot to the location would be updating multiple tables in postgresql further of updates which the connected desires to be made. Round update should certify two things: An missing of which row should be outdated New missing for one or more has Going back to our first encounter: MultiRow, we would updating multiple tables in postgresql Each encounter is a two-element route.

MultiRow is stimulating so postgersql buttons which are going across different SQL databases are encountered in a appointment constabulary, and approaches which only amount for star SQL databases are let in a small. An confrontation of the time summoners war not updating is instantiated when the call is made, and well then passed to updating multiple tables in postgresql constabulary mlutiple to the database in use.

If there is no database-specific star for the database in use, then DBIx:: MultiRow will grasp use the about class updting implements has that should work for any SQL database. At the other u;dating care, the only database-specific favour is for PostgreSQL. As are a few more details worth mentioning.

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5 Comments

  1. Make sure you are connected to the encyclopedia database. If omitted, PostgreSQL will update every row in the target table, so before executing such a query be sure that this is actually what you want to do. Both should hold strings of up to characters.

  2. This is in fact entirely possible in many database systems. We previously set all users to be disabled.

  3. We'll want to use the current data in the users table in the next section. Delete all Rows It's rare that you will want to delete all the rows in a table. It is relatively straightforward to populate a table with multiple rows with just one query or at least, far fewer queries than the number of rows desired.

  4. Remove all the rows from the countries table. Let's delete one of the rows that contain our duplicate name. We've now covered the various statements needed to create and work with single tables in a database.

  5. So we could think in terms of creating a re-usable module which would implement that logic.

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