--- title: "9: Casting and aliases | SurrealDB University" description: "Follow along with interactive SurrealDB lessons featuring hands-on exercises, code examples, and step-by-step instructions." url: https://surrealdb.com/learn/tour/page-09 --- ![Course content preview](https://surrealdb.com/assets/static/town.D95IYf2V.avif) [Back to Courses](https://surrealdb.com/learn) Course chapters [Welcome to the Tour of SurrealDB!](https://surrealdb.com/learn/tour) [1: Connecting to a database](https://surrealdb.com/learn/tour/page-01) [2: Creating records](https://surrealdb.com/learn/tour/page-02) [3: Using the ONLY keyword](https://surrealdb.com/learn/tour/page-03) [4: Non-ASCII record IDs](https://surrealdb.com/learn/tour/page-04) [5: Parentheses, indexing, and accessing fields](https://surrealdb.com/learn/tour/page-05) [6: Deleting records](https://surrealdb.com/learn/tour/page-06) [7: Field order in objects](https://surrealdb.com/learn/tour/page-07) [8: Tips when selecting records](https://surrealdb.com/learn/tour/page-08) [9: Casting and aliases](https://surrealdb.com/learn/tour/page-09) [10: Affixes](https://surrealdb.com/learn/tour/page-10) [11: Updating records](https://surrealdb.com/learn/tour/page-11) [12: Linking records](https://surrealdb.com/learn/tour/page-12) [13: Viewing the database as a whole](https://surrealdb.com/learn/tour/page-13) [14: Schemafull and schemaless](https://surrealdb.com/learn/tour/page-14) [15: Viewing the schema](https://surrealdb.com/learn/tour/page-15) [16: Literal types and assertions](https://surrealdb.com/learn/tour/page-16) [17: INSERT and using JSON](https://surrealdb.com/learn/tour/page-17) [18: FOR loops](https://surrealdb.com/learn/tour/page-18) [19: Basic graph relations](https://surrealdb.com/learn/tour/page-19) [20: Creating graph edges](https://surrealdb.com/learn/tour/page-20) [21: Querying graph relations](https://surrealdb.com/learn/tour/page-21) [22: Graph relations at greater depth](https://surrealdb.com/learn/tour/page-22) [23: Adding and improving data](https://surrealdb.com/learn/tour/page-23) [24: Defining events](https://surrealdb.com/learn/tour/page-24) [25: Defining indexes](https://surrealdb.com/learn/tour/page-25) [26: Improving the schema](https://surrealdb.com/learn/tour/page-26) [27: Visualising graph paths](https://surrealdb.com/learn/tour/page-27) [28: Recursive queries: setup](https://surrealdb.com/learn/tour/page-28) [29: Recursive queries](https://surrealdb.com/learn/tour/page-29) [30: More on recursive queries](https://surrealdb.com/learn/tour/page-30) [31: AI vector search](https://surrealdb.com/learn/tour/page-31) [Done the tour!](https://surrealdb.com/learn/tour/page-32) # 9: Casting and aliases SurrealDB has a lot of [data types](https://surrealdb.com/docs/reference/query-language/language-primitives/data-types), with names in lowercase such as `bool`, `number`, `string`, and `array`. Most types can be quickly changed into another by using a [casting function](https://surrealdb.com/docs/reference/query-language/language-primitives/casting). To cast into another type, put the target type inside `<>` angle brackets to the left. ``` SELECT name, address, -- 'floors' is a number, output as a string instead floorsFROM place; ``` ![Surrealist Icon](https://surrealdb.com/assets/static/fdfe2c20f5941d5e.D0guSOhZ.webp) Run Query One of the fields is called `" floors"`, because by default a field with a value set by an operation will have the operation as its name. Response ```surql [ { " floors": '8', address: '2025 Statement Street, Riverdale', name: 'Surreal Library' } ] ``` If you find this field name ugly or want to rename it for another reason, you can use `AS` to give it a different name (give it an alias). ``` SELECT name, address, floors AS floorsFROM place; ``` ![Surrealist Icon](https://surrealdb.com/assets/static/fdfe2c20f5941d5e.D0guSOhZ.webp) Run Query Response ```surql [ { address: '2025 Statement Street, Riverdale', floors: '8', name: 'Surreal Library' } ] ``` Casting will only work as long as the input is valid, mind you. ``` -- Works fine'1859-11-26';-- Invalid input for datetime'EIGHTEEN FIFTY NINE, NOVEMBER TWENTY SIX';-- A bool can only be 'true' or 'false'"Hello there!"; ``` ![Surrealist Icon](https://surrealdb.com/assets/static/fdfe2c20f5941d5e.D0guSOhZ.webp) Run Query Outputs ```surql -------- Query 1 -------- d'1859-11-26T00:00:00Z' -------- Query 2 -------- "Expected a datetime but cannot convert 'EIGHTEEN FIFTY NINE, NOVEMBER TWENTY SIX' into a datetime" -------- Query 3 -------- "Expected a bool but cannot convert 'Hello there!' into a bool" ``` Casting also won't work for complex types because the database can't tell what you want to do. Take this object for example that you would like to turn into an array. ```surql /** [test] [[test.results]] error = "Could not cast into `array` using input `{ address: '2025 Statement Street, Riverdale', floors: '8', name: 'Surreal Library' }`" */ -- This cast won't work { address: '2025 Statement Street, Riverdale', floors: '8', name: 'Surreal Library' }; ``` You might want an array holding each key, or arrays holding each key and value, and so on. In this case, take a look at SurrealDB's [object functions](https://surrealdb.com/docs/reference/query-language/functions/database-functions/object) to choose how to transform from one type into another. For example, you could use the `object::values()` function to just return the object's values. ``` -- Regular function syntaxobject::values({ address: '2025 Statement Street, Riverdale', floors: '8', name: 'Surreal Library'});-- Method syntax: same function, same result{ address: '2025 Statement Street, Riverdale', floors: '8', name: 'Surreal Library'}.values(); ``` ![Surrealist Icon](https://surrealdb.com/assets/static/fdfe2c20f5941d5e.D0guSOhZ.webp) Run Query Array of the object's values ```surql [ '2025 Statement Street, Riverdale', '8', 'Surreal Library' ] ``` Or you could use [`object::from_entries()`](https://surrealdb.com/docs/reference/query-language/functions/database-functions/object#objectfrom_entries) to do the opposite: constructing an object from arrays of arrays. ``` object::from_entries([ [ 'address', '2025 Statement Street, Riverdale' ], [ 'floors', '8' ], [ 'name', 'Surreal Library' ]]); ``` ![Surrealist Icon](https://surrealdb.com/assets/static/fdfe2c20f5941d5e.D0guSOhZ.webp) Run Query Response ```surql { address: '2025 Statement Street, Riverdale', floors: '8', name: 'Surreal Library' } ``` The [`array::map()`](https://surrealdb.com/docs/reference/query-language/functions/database-functions/array#arraymap) function is another great way to turn one type into another. After typing `.map()`, choose a parameter name inside `||` for each item, and then choose what to do with each item before passing it on. This example of the function takes two strings and turns each one of them into an object with three fields. The output is an array of objects created by each string. ``` ["Surreal Library", "Riverdale"].map(|$name| { name: $name, is_cool: true, name_is_long: $name.len() > 10}); ``` ![Surrealist Icon](https://surrealdb.com/assets/static/fdfe2c20f5941d5e.D0guSOhZ.webp) Run Query Response ```surql [ { is_cool: true, name: 'Surreal Library', name_is_long: true }, { is_cool: true, name: 'Riverdale', name_is_long: false } ] ``` Previous 8: Tips when selecting records [Previous](https://surrealdb.com/learn/tour/page-08) Next lesson 10: Affixes [Next lesson](https://surrealdb.com/learn/tour/page-10) ```json {"@context":"https://schema.org","@type":"Course","name":"Welcome to the Tour of SurrealDB!","description":"Welcome to the Tour of SurrealDB!","url":"https://surrealdb.com/learn/tour","inLanguage":"en","isAccessibleForFree":true,"provider":{"@type":"Organization","name":"SurrealDB","url":"https://surrealdb.com"},"hasPart":[{"@type":"LearningResource","name":"Welcome to the Tour of 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