![]() What is the data type precedence? If the value’s data type is already at a higher precedence, it won’t be implicitly converted to a lower one.Įxplicit Type Conversions with CAST AND CONVERT.Can a value be converted from one data type to another? Implicit conversion isn’t supported for all data types, so understanding whether certain combinations work, is important to understand.There are really two factors that take place to determine whether an item can be implicitly converted to a data type: ‘Today is ‘ isn’t a valid date, SQL doesn’t know where that exists on any calendar, so throws an error. You would think this statement would return a result since it seems it would not be difficult to convert the current data and time to a text value, but because DATETIME has a higher precedence than any textual value, SQL is trying to convert the text to a date. The result we’re aiming for is ‘Today is 08:01:54.932’ or something similar, yet the statement returns this error Msg 241, Level 16, State 1, Line 1Ĭonversion failed when converting date and/or time from character string. Now Consider SELECT 'Today is ' + GETDATE() Since converting from 100 to 100.00 is an allowed implicit conversion, it occurs without error. 5 is a higher precedence, so SQL converts 100, which is an INT type, to the higher precedence. Note: With 30 or more supported data types, the official list is longer.ĭata types of lower precedence will attempt to convert to one of higher precedence, but not the other way around. Here is the order of precedence for the common data types we have previously covered: The reason is that order values are implicitly converted from one data type to another is determined by type precedence.ĭata type precedence determines the direction or order implicit datatype occur. You may be wondering why Quantity was converted to Money and not StandardCost to SMALLINT. In this case the Quantity was first converted to a MONEY datatype before the TotalCost was calculated. When you review the results you see that total cost has decimal places? Implicit Conversion Results One is an SMALLINT value, which has no decimal places, and the other is MONEY, which does. In this example we’re multiplying Quantity by Standard cost. For example, the VARCHAR value ‘The car broke down’ never makes a good DATETIME.Īn example of an implicit data conversion occurs when we work with percentages and INT data types. Please keep in mind this chart shows what implicit conversions are possible, it doesn’t guarantee all values from one type will convert to another. The following chart shows what can be implicitly converted for the common data types we’ve previously covered: SQL Conversion Functions – Allowed Implicit Datatype Conversions. Not all values can be implicitly converted to another data type. Implicit conversions are those conversions that occur automatically whenever the CAST or CONVERT functions aren’t used. Explicit Type Conversions with CAST AND CONVERT.
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