Updating data

Now that we’ve returned from selecting things, it’s time to update our knowledge of the UPDATE statement.

We’ll cover:

• How to update one record, a range of records, or the entire table
• The four different methods for updating data

Starting where we left off in our previous lesson on inserting data.

Update with INSERT

We briefly touched on how both the INSERT and UPSERT statements both INSERT and UPDATE.

Let’s expand a bit on the example of how to UPDATE with the INSERT statement before moving on to the UPDATE statement.

INSERT INTO product (id)
VALUES (1),(1) ON DUPLICATE KEY UPDATE colours += ['Purple'];

INSERT INTO product (id, colours) 
VALUES (2, ['Pink']), (2, ['Dark Heather Grey','Bubble Gum Pink', 'Purple'])
ON DUPLICATE KEY UPDATE colours = $input.colours;

We saw the first example in the previous lesson, but there is also another way to UPDATE data using the $input parameter. Here the $input parameter is an object that gives us access to all the fields of the record we are attempting to insert. We can therefore use the dot notation to select the sizes field that we are inserting and use that to update the sizes field that already exists.

While this is possible if you need it, the UPDATE statement generally has a much better developer experience for updating, as we’ll see.

The four different methods for updating data

-- Update the currency field in the entire product table
UPDATE product SET currency = "USD";
UPDATE product MERGE {currency: "USD"};
UPDATE product PATCH [{
		op: "replace",
		path: "currency",
		value: "USD"
}];

-- Update the entire product table to contain only the currency field
UPDATE product CONTENT {currency: "USD"};
-- Replace is an Alias for CONTENT
UPDATE product REPLACE {currency: "USD"};

Now we mentioned that we have 4 different methods, but you’re seeing 5 update statements here, let’s explain.

We have SET, MERGE and PATCH, which can update individual fields in a record. Here we are updating the currency field in the entire product table.

• SET uses familiar SQL syntax
• MERGE does the same thing just using a JSON-like syntax
• PATCH also does the same thing, just using the JSON Patch specification

The JSON Patch specification is a proposed standard by the Internet Engineering Task Force (IETF).

The purpose is to avoid sending a whole document when only a part has changed, used in combination with the HTTP PATCH method. Allowing for partial updates for HTTP APIs in a standards-compliant way.

Therefore we have:

• MERGE which sends partial documents in our own simplified way
• PATCH which sends partial documents in a standards-compliant way
  • It is more flexible than MERGE but with a somewhat more complex syntax

Moving on to CONTENT and REPLACE. They are both the same thing, as REPLACE is just an alias for CONTENT.

What they do, however, is always send the whole document. Which means it effectively replaces the CONTENT that was there previously.

-- Update a single record
UPDATE product:01GRTTE7DG94R864R67MGDT0QM SET
	colours -= "Pink",
	colours += "Bubble Gum Pink",
	time.updated_at = time::now();

UPDATE product:01GRTTE7DG94R864R67MGDT0QM PATCH [
	{
		op: "remove",
		path: "colours/1"
	},
	{
		op: "add",
		path: "colours",
		value: "Bubble Gum Pink"
	},
	{
		op: "replace",
		path: "time.updated_at",
		value: time::now()
	}
];

Let’s explore another, more realistic example. Here we are updating a single record, which again, is the hoodie I’m currently wearing. We used to have this hoodie in the pink colour on our SurrealDB.store, but the manufacturer stopped using that colour, which meant we needed another pink colour, the Bubble Gum Pink.

Therefore, we need to update the product table in our fictional Surreal Deal Store to reflect that.

As we’re replacing just an item in an array, we cannot use MERGE as it only works on entire fields, including nested fields inside objects like time.updated_at as long as you put the field path in quotes “time.updated_at": time::now().

We are then left with SET and PATCH, where we remove the pink colour from the array, add Bubble Gum Pink and finally update the updated_at time. We could simplify our PATCH to only use two replace operations, but I separated it into remove and add just for educational purposes here.

-- Update a range of records with record IDs (recommended if possible)
UPDATE
	product:01FZ0CR6N09V5RG9RQ9A3264GX..=01G0MW4VTG8QZR3A4BTEXHXWS7
SET currency = "USD", time.updated_at = time::now();

-- Update a range of records with the where clause
UPDATE product
SET currency = "USD", time.updated_at = time::now()
WHERE time.created_at >= d"2022-10-19T00:01:53Z"
AND time.created_at <= d"2022-10-26T18:00:05Z";

You can also UPDATE a range of records, either by using record ranges or the where clause.

Whenever you can, always use record IDs as that is the most efficient way.

The UPDATE statement is also used to DELETE fields, but we’ll cover that in the next lesson on deleting data.

Summary

Now that we’ve updated our knowledge of the UPDATE statement, let’s summarise what we’ve learned.

• The UPDATE statement
  • Can update one record, a range of records, or the entire table.
  • There are four different methods for updating data
    • Using SET for a SQL-like experience
    • Using MERGE to merge-update only specific fields within a record like SET
    • Using CONTENT or its alias REPLACE to completely replace the record data
    • Using PATCH to use the JSON patch format for partial updates. Allowing for partial updates for HTTP APIs in a standards-compliant way.
  • Finally, it can also DELETE fields (covered in the next lesson on deleting data).