Merge pull request #39533 from ClickHouse/now-in-block

Add function `nowInBlock`

docs/en/sql-reference/functions/date-time-functions.md

@@ -836,7 +836,7 @@ Result:
 
 ## now
 
-Returns the current date and time.
+Returns the current date and time at the moment of query analysis. The function is a constant expression.
 
 **Syntax**
 
@@ -884,14 +884,20 @@ Result:
 └──────────────────────┘
 ```
 
+## nowInBlock
+
+Returns the current date and time at the moment of processing of each block of data. In contrast to the function `now`, it is not a constant expression, and the returned value will be different in different blocks for long-running queries.
+
+It makes sense to use this function to generate the current time in long-running INSERT SELECT queries.
+
 ## today
 
-Accepts zero arguments and returns the current date at one of the moments of request execution.
+Accepts zero arguments and returns the current date at one of the moments of query analysis.
 The same as ‘toDate(now())’.
 
 ## yesterday
 
-Accepts zero arguments and returns yesterday’s date at one of the moments of request execution.
+Accepts zero arguments and returns yesterday’s date at one of the moments of query analysis.
 The same as ‘today() - 1’.
 
 ## timeSlot

src/Functions/blockNumber.cpp

@@ -44,7 +44,10 @@ public:
         return 0;
     }
 
-    bool isDeterministic() const override { return false; }
+    bool isDeterministic() const override
+    {
+        return false;
+    }
 
     bool isDeterministicInScopeOfQuery() const override
     {

src/Functions/now.cpp

@@ -3,7 +3,6 @@
 #include <Functions/IFunction.h>
 #include <Core/DecimalFunctions.h>
 #include <Functions/FunctionFactory.h>
-#include <Core/Field.h>
 
 #include <Functions/extractTimeZoneFromFunctionArguments.h>
 

src/Functions/nowInBlock.cpp

@@ -0,0 +1,88 @@
+#include <Functions/IFunction.h>
+#include <Functions/FunctionFactory.h>
+#include <Functions/extractTimeZoneFromFunctionArguments.h>
+#include <DataTypes/DataTypeDateTime.h>
+#include <Columns/ColumnsNumber.h>
+
+
+namespace DB
+{
+
+namespace ErrorCodes
+{
+    extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
+    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
+}
+
+namespace
+{
+
+/** Returns current time at calculation of every block.
+  * In contrast to 'now' function, it's not a constant expression and is not a subject of constant folding.
+  */
+class FunctionNowInBlock : public IFunction
+{
+public:
+    static constexpr auto name = "nowInBlock";
+    static FunctionPtr create(ContextPtr)
+    {
+        return std::make_shared<FunctionNowInBlock>();
+    }
+
+    String getName() const override
+    {
+        return name;
+    }
+
+    bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override
+    {
+        return false;
+    }
+
+    /// Optional timezone argument.
+    bool isVariadic() const override { return true; }
+
+    size_t getNumberOfArguments() const override { return 0; }
+
+    bool isDeterministic() const override
+    {
+        return false;
+    }
+
+    bool isDeterministicInScopeOfQuery() const override
+    {
+        return false;
+    }
+
+    DataTypePtr getReturnTypeImpl(const ColumnsWithTypeAndName & arguments) const override
+    {
+        if (arguments.size() > 1)
+        {
+            throw Exception("Arguments size of function " + getName() + " should be 0 or 1", ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
+        }
+        if (arguments.size() == 1 && !isStringOrFixedString(arguments[0].type))
+        {
+            throw Exception(
+                "Arguments of function " + getName() + " should be String or FixedString", ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
+        }
+        if (arguments.size() == 1)
+        {
+            return std::make_shared<DataTypeDateTime>(extractTimeZoneNameFromFunctionArguments(arguments, 0, 0));
+        }
+        return std::make_shared<DataTypeDateTime>();
+    }
+
+    ColumnPtr executeImpl(const ColumnsWithTypeAndName &, const DataTypePtr &, size_t input_rows_count) const override
+    {
+        return ColumnUInt32::create(input_rows_count, time(nullptr));
+    }
+};
+
+}
+
+void registerFunctionNowInBlock(FunctionFactory & factory)
+{
+    factory.registerFunction<FunctionNowInBlock>();
+}
+
+}

src/Functions/registerFunctionsDateTime.cpp

@@ -43,6 +43,7 @@ void registerFunctionToRelativeMinuteNum(FunctionFactory &);
 void registerFunctionToRelativeSecondNum(FunctionFactory &);
 void registerFunctionToTime(FunctionFactory &);
 void registerFunctionNow(FunctionFactory &);
+void registerFunctionNowInBlock(FunctionFactory &);
 void registerFunctionNow64(FunctionFactory &);
 void registerFunctionToday(FunctionFactory &);
 void registerFunctionYesterday(FunctionFactory &);
@@ -126,6 +127,7 @@ void registerFunctionsDateTime(FunctionFactory & factory)
     registerFunctionToTime(factory);
     registerFunctionNow(factory);
     registerFunctionNow64(factory);
+    registerFunctionNowInBlock(factory);
     registerFunctionToday(factory);
     registerFunctionYesterday(factory);
     registerFunctionTimeSlot(factory);

tests/queries/0_stateless/02372_now_in_block.reference

@@ -0,0 +1,2 @@
+2
+1

tests/queries/0_stateless/02372_now_in_block.sql

@@ -0,0 +1,4 @@
+SELECT count() FROM (SELECT DISTINCT nowInBlock(), nowInBlock('Pacific/Pitcairn') FROM system.numbers LIMIT 2);
+SELECT nowInBlock(1); -- { serverError 43 }
+SELECT nowInBlock(NULL) IS NULL;
+SELECT nowInBlock('UTC', 'UTC'); -- { serverError 42 }