gengliangwang commented on a change in pull request #33516:
URL: https://github.com/apache/spark/pull/33516#discussion_r676771658
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File path: docs/sql-ref-ansi-compliance.md
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@@ -160,6 +160,81 @@ SELECT * FROM t;
+---+
```
+### Type coercion
+#### Type Promotion and Precedence
+When `spark.sql.ansi.enabled` is set to `true`, Spark SQL uses several rules
that govern how conflicts between data types are resolved.
+At the heart of this conflict resolution is the Type Precedence List which
defines whether values of a given data type can be promoted to another data
type implicitly.
+
+| Data type | precedence list(from narrowest to widest)
|
+|-----------|------------------------------------------------------------------|
+| Byte | Byte -> Short -> Int -> Long -> Decimal -> Float* -> Double
|
+| Short | Short -> Int -> Long -> Decimal-> Float* -> Double
|
+| Int | Int -> Long -> Decimal -> Float* -> Double
|
+| Long | Long -> Decimal -> Float* -> Double
|
+| Decimal | Decimal -> Float* -> Double
|
+| Float | Float -> Double
|
+| Double | Double
|
+| Date | Date-> Timestamp
|
+| Timestamp | Timestamp
|
+| String | String
|
+| Binary | Binary
|
+| Boolean | Boolean
|
+| Interval | Interval
|
+| Map | Map**
|
+| Array | Array**
|
+| Struct | Struct**
|
+
+\* For least common type resolution float is skipped to avoid loss of
precision.
+
+\*\* For a complex type, the precedence rule applies recursively to its
component elements.
+
+Special rules apply for string literals and untyped NULL.
+A NULL can be promoted to any other type, while a string literal can be
promoted to any simple data type.
+
+This is a graphical depiction of the precedence list as a directed tree:
+<img src="img/type-precedence-list.png" width="80%" title="Type Precedence
List" alt="Type Precedence List">
+
+#### Least Common Type Resolution
+The least common type from a set of types is the narrowest type reachable from
the precedence list by all elements of the set of types.
+
+The least common type resolution is used to:
+- Decide whether a function expecting a parameter of a type can be invoked
using an argument of a narrower type.
+- Derive the argument type for functions which expect a shared argument type
for multiple parameters, such as coalesce, least, or greatest.
Review comment:
Done(BTW the extra space will be omitted in web page anyway)
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