{"id":28276,"date":"2022-12-28T12:15:08","date_gmt":"2022-12-28T02:15:08","guid":{"rendered":"https:\/\/database.guide\/?p=28276"},"modified":"2022-12-28T12:15:08","modified_gmt":"2022-12-28T02:15:08","slug":"redis-zdiffstore-command-explained","status":"publish","type":"post","link":"https:\/\/database.guide\/redis-zdiffstore-command-explained\/","title":{"rendered":"Redis ZDIFFSTORE Command Explained"},"content":{"rendered":"\n

In Redis, the ZDIFFSTORE<\/code> command computes the difference between the first and all successive input sorted sets and stores the result in the specified key.<\/p>\n\n\n\n

ZDIFFSTORE<\/code> works in the same way as the ZDIFF<\/a><\/code> command, except that it stores the result instead of returning it (ZDIFF<\/code> returns the result instead of storing it in a new key).<\/p>\n\n\n\n\n\n\n\n

Syntax<\/h2>\n\n\n\n

The syntax goes like this:<\/p>\n\n\n\n

ZDIFFSTORE destination numkeys key [key ...]<\/code><\/pre>\n\n\n\n
Example<\/h2>\n\n\n\n
Suppose we create two sorted sets, like this:<\/p>\n\n\n\n
ZADD cats 1 meow 2 fluffy 3 scratch<\/code><\/pre>\n\n\n\n
And:<\/p>\n\n\n\n
ZADD dogs 1 bark 2 woof 3 fluffy<\/code><\/pre>\n\n\n\n
We can use the ZDIFFSTORE<\/code> command against those two sorted sets like this:<\/p>\n\n\n\n
ZDIFFSTORE result1 2 cats dogs<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
(integer) 2<\/pre>\n\n\n\n
That computed all the elements in the first set that aren’t in the second set and stored it in a key called result1<\/code>. We got an integer reply of 2<\/code>, which means that two elements were added to the resulting sorted set.<\/p>\n\n\n\n
Let’s take a look at the new key:<\/p>\n\n\n\n
ZRANGE result1 0 -1<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
1) \"meow\"\n2) \"scratch\"<\/pre>\n\n\n\n
As expected, it only contains two elements. That’s because fluffy<\/code> appears in both of the original sorted sets and ZDIFFSTORE<\/code> only returns the difference between the first sorted set and all subsequent sorted sets.<\/p>\n\n\n\n
The numkeys<\/code><\/em> value of 2<\/code> in the above examples means that I’m providing two sets.<\/p>\n\n\n\n
More Sorted Sets<\/h2>\n\n\n\n
The ZDIFFSTORE<\/code> command allows us to include as many sorted sets as we want in our list. They are all compared to the first one and any difference between the first and subsequent sets are returned.<\/p>\n\n\n\n
Let’s create another sorted set:<\/p>\n\n\n\n
ZADD birds 1 tweet 2 scratch<\/code><\/pre>\n\n\n\n
Now let’s run ZDIFFSTORE<\/code> against all three sets:<\/p>\n\n\n\n
ZDIFFSTORE result2 3 cats dogs birds<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
(integer) 1<\/pre>\n\n\n\n
Note that the numkeys<\/code><\/em> argument is now 3<\/code>, which reflects the number of sorted sets I’m providing.<\/p>\n\n\n\n
This time only one element is added to the new sorted set. That’s because the other elements from the cats<\/code> set contain values that are also present in at least one of the other sorted sets. That is, the dogs<\/code> set contains fluffy<\/code> and the birds<\/code> set contains scratch<\/code>, both of which are in the cats<\/code> set.<\/p>\n\n\n\n
Let’s take a look at the new sorted set:<\/p>\n\n\n\n
ZRANGE result2 0 -1<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
1) \"meow\"<\/pre>\n\n\n\n
Non-Existent Keys<\/h2>\n\n\n\n
Keys that don’t exist are treated as empty sets:<\/p>\n\n\n\n
ZDIFFSTORE result3 2 oops1 oops2<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
(integer) 0<\/pre>\n\n\n\n
Nothing was added to the new key. <\/p>\n\n\n\n
Let’s check the new key:<\/p>\n\n\n\n
ZRANGE result3 0 -1<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
(empty array)<\/pre>\n\n\n\n
The key contains an empty array because none of the keys that we used with ZDIFFSTORE<\/code> existed.<\/p>\n\n\n\n
Here’s what happens when the first key exists, but none of the others do:<\/p>\n\n\n\n
ZDIFFSTORE result4 3 cats oops1 oops2<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
(integer) 3<\/pre>\n\n\n\n
And take a look at the key:<\/p>\n\n\n\n
ZRANGE result4 0 -1<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
1) \"meow\"\n2) \"fluffy\"\n3) \"scratch\"<\/pre>\n\n\n\n
All elements from the first set were added to the new key because none of those elements are present in any of the other (empty) sets.<\/p>\n\n\n\n
Using the Wrong numkeys<\/em><\/code> Argument<\/h2>\n\n\n\n
Here’s what happens when we use the wrong value for the numkeys<\/em><\/code> argument:<\/p>\n\n\n\n
ZDIFFSTORE result5 3 cats dogs<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
(error) ERR syntax error<\/pre>\n\n\n\n
In this case I specified that there would be three sorted sets to compare, but I only provided two.<\/p>\n\n\n\n
The same error applies when it’s the other way around (i.e. I specify 2<\/code> but provide three keys):<\/p>\n\n\n\n
ZDIFFSTORE result6 2 cats dogs birds<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
(error) ERR syntax error<\/pre>\n\n\n\n
Passing a Key of the Wrong Type<\/h2>\n\n\n\n
Here’s what happens when we pass a key that contains a different type (i.e. it’s not a sorted set):<\/p>\n\n\n\n
ZDIFFSTORE result7 2 cats country<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
(error) WRONGTYPE Operation against a key holding the wrong kind of value<\/pre>\n\n\n\n
In this case, the country<\/code> key contains a string.<\/p>\n\n\n\n
However, it works fine on non-sorted sets:<\/p>\n\n\n\n
ZDIFFSTORE result8 2 countries cats<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
(integer) 2<\/pre>\n\n\n\n
In this case the countries<\/code> key contains a (non-sorted) set as follows:<\/p>\n\n\n\n
ZRANGE result8 0 -1<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
1) \"Australia\"\n2) \"New Zealand\"<\/pre>\n\n\n\n
When the Destination Key Already Exists<\/h2>\n\n\n\n
If the destination key already exists, it’s overwritten.<\/p>\n\n\n\n
Let’s overwrite the result8<\/code> key from the previous example:<\/p>\n\n\n\n
ZDIFFSTORE result8 2 cats dogs<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
(integer) 2<\/pre>\n\n\n\n
Check the contents:<\/p>\n\n\n\n
ZRANGE result8 0 -1<\/code><\/pre>\n\n\n\n
Result:<\/p>\n\n\n\n
1) \"meow\"\n2) \"scratch\"<\/pre>\n\n\n\n
As expected, the result8<\/code> key has been overwritten with our new results.<\/p>\n","protected":false},"excerpt":{"rendered":"
In Redis, the ZDIFFSTORE command computes the difference between the first and all successive input sorted sets and stores the result in the specified key. ZDIFFSTORE works in the same way as the ZDIFF command, except that it stores the result instead of returning it (ZDIFF returns the result instead of storing it in a … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[153],"tags":[154,20],"class_list":["post-28276","post","type-post","status-publish","format-standard","hentry","category-redis","tag-commands","tag-what-is"],"_links":{"self":[{"href":"https:\/\/database.guide\/wp-json\/wp\/v2\/posts\/28276","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/database.guide\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/database.guide\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/database.guide\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/database.guide\/wp-json\/wp\/v2\/comments?post=28276"}],"version-history":[{"count":5,"href":"https:\/\/database.guide\/wp-json\/wp\/v2\/posts\/28276\/revisions"}],"predecessor-version":[{"id":28284,"href":"https:\/\/database.guide\/wp-json\/wp\/v2\/posts\/28276\/revisions\/28284"}],"wp:attachment":[{"href":"https:\/\/database.guide\/wp-json\/wp\/v2\/media?parent=28276"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/database.guide\/wp-json\/wp\/v2\/categories?post=28276"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/database.guide\/wp-json\/wp\/v2\/tags?post=28276"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}