dialect with interval style

datafusion/sql/src/unparser/dialect.rs

@@ -42,6 +42,9 @@ pub trait Dialect {
         false
     }
 
+    fn interval_style(&self) -> IntervalStyle {
+        IntervalStyle::PostgresVerbose
+    }
     // Does the dialect use DOUBLE PRECISION to represent Float64 rather than DOUBLE?
     // E.g. Postgres uses DOUBLE PRECISION instead of DOUBLE
     fn use_double_precision_for_float64(&self) -> bool {
@@ -55,6 +58,22 @@ pub trait Dialect {
         false
     }
 }
+
+/// `IntervalStyle` to use for unparsing
+///
+/// https://www.postgresql.org/docs/current/datatype-datetime.html#DATATYPE-INTERVAL-INPUT
+/// different DBMS follows different standards, popular ones are:
+/// postgres_verbose: '2 years 15 months 100 weeks 99 hours 123456789 milliseconds' which is
+/// compatible with arrow display format, as well as duckdb
+/// sql standard format is '1-2' for year-month, or '1 10:10:10.123456' for day-time
+/// https://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt
+#[derive(Clone, Copy)]
+pub enum IntervalStyle {
+    PostgresVerbose,
+    SQLStandard,
+    MySQL,
+}
+
 pub struct DefaultDialect {}
 
 impl Dialect for DefaultDialect {
@@ -77,6 +96,10 @@ impl Dialect for PostgreSqlDialect {
         Some('"')
     }
 
+    fn interval_style(&self) -> IntervalStyle {
+        IntervalStyle::PostgresVerbose
+    }
+
     fn use_double_precision_for_float64(&self) -> bool {
         true
     }
@@ -93,6 +116,10 @@ impl Dialect for MySqlDialect {
         false
     }
 
+    fn interval_style(&self) -> IntervalStyle {
+        IntervalStyle::MySQL
+    }
+
     fn use_char_for_utf8_cast(&self) -> bool {
         true
     }
@@ -110,6 +137,7 @@ pub struct CustomDialect {
     identifier_quote_style: Option<char>,
     supports_nulls_first_in_sort: bool,
     use_timestamp_for_date64: bool,
+    interval_style: IntervalStyle,
     use_double_precision_for_float64: bool,
     use_char_for_utf8_cast: bool,
 }
@@ -120,6 +148,7 @@ impl Default for CustomDialect {
             identifier_quote_style: None,
             supports_nulls_first_in_sort: true,
             use_timestamp_for_date64: false,
+            interval_style: IntervalStyle::SQLStandard,
             use_double_precision_for_float64: false,
             use_char_for_utf8_cast: false,
         }
@@ -149,6 +178,10 @@ impl Dialect for CustomDialect {
         self.use_timestamp_for_date64
     }
 
+    fn interval_style(&self) -> IntervalStyle {
+        self.interval_style
+    }
+
     fn use_double_precision_for_float64(&self) -> bool {
         self.use_double_precision_for_float64
     }
@@ -163,6 +196,7 @@ pub struct CustomDialectBuilder {
     identifier_quote_style: Option<char>,
     supports_nulls_first_in_sort: bool,
     use_timestamp_for_date64: bool,
+    interval_style: IntervalStyle,
     use_double_precision_for_float64: bool,
     use_char_for_utf8_cast: bool,
 }
@@ -173,6 +207,7 @@ impl CustomDialectBuilder {
             identifier_quote_style: None,
             supports_nulls_first_in_sort: true,
             use_timestamp_for_date64: false,
+            interval_style: IntervalStyle::PostgresVerbose,
             use_double_precision_for_float64: false,
             use_char_for_utf8_cast: false,
         }
@@ -183,6 +218,7 @@ impl CustomDialectBuilder {
             identifier_quote_style: self.identifier_quote_style,
             supports_nulls_first_in_sort: self.supports_nulls_first_in_sort,
             use_timestamp_for_date64: self.use_timestamp_for_date64,
+            interval_style: self.interval_style,
             use_double_precision_for_float64: self.use_double_precision_for_float64,
             use_char_for_utf8_cast: self.use_char_for_utf8_cast,
         }
@@ -209,6 +245,11 @@ impl CustomDialectBuilder {
         self
     }
 
+    pub fn with_interval_style(mut self, interval_style: IntervalStyle) -> Self {
+        self.interval_style = interval_style;
+        self
+    }
+
     pub fn with_use_double_precision_for_float64(
         mut self,
         use_double_precision_for_float64: bool,