问sql脚本变量默认值

EN

:on error ignore -- Ensures that sqlcmd.exe will not fail when referencing an undefined scripting variable. Remove this if you want your script to work in SSMS in regular mode, too.
Declare @valueOrDefault as nvarchar(max)= N'$(value)';    
if @valueOrDefault = N'$' + N'(value)' set @valueOrDefault = N'default value'; -- Test if there is a value and, if not, assign a default; note the splitting of the reference string to avoid expansion.

-- use @valueOrDefault from now on

-- Store the default value in the context info (session-level storage accessible across batches that holds up to 128 bytes).
declare @binDefaultValue varbinary(128)= CAST(N'default value' AS varbinary(128));
set CONTEXT_INFO @binDefaultValue;
go -- Make the set CONTEXT_INFO statement take effect.

-- If the scripting variable has a value, store ITS value in the context info instead.
:on error ignore -- Temporarily ignore errors so that accessing a non-existent scripting variable doesn't abort the entire script.
    declare @value as nvarchar(max) = N'$(value)'; -- Try to access the scripting variable; thanks to :on error ignore this will only give a warning.
    if @value <> N'$' + N'(value)' -- Test if there is a value; note the splitting of the reference string to avoid expansion.
    begin
    -- We have a scripting-variable value: Store it in the context info (replacing the default value).
        declare @binValue as varbinary(128) = cast(@value as varbinary(128));
        set CONTEXT_INFO @binValue;
    end
go -- End batch here, so we can switch back to :on error exit (requires a new batch).

:on error exit -- New batch: switch back to robust error handling.
-- End the batch here, so that SSMS in *regular* mode - which will fail on the line above - continues processing below.
-- Note that when run by sqlcmd.exe the subsequent batches will inherit :on error exit.
go

-- Retrieve the value or default value from the context info...
declare @valueOrDefault as nvarchar(max) = convert(nvarchar(max), CONTEXT_INFO(), 0);
-- ... and remove trailing null characters. ?? Is there an easier way to do this?
declare @pos as int = 0;
while @pos < LEN(@valueOrDefault)
begin
    set @pos=@pos+1
    if UNICODE(substring(@valueOrDefault, @pos, 1)) = 0  break;
end
if @pos > 0 set @valueOrDefault = left(@valueOrDefault, @pos - 1);

-- @valueOrDefault now contains the scripting-variable value or default value.
print 'Value or default value: [' + @valueOrDefault + ']';

BEGIN TRY 
    DECLARE @bogusVar VARCHAR(64);
    SET @bogusVar = '' + $(envVar);
    PRINT 'Using values passed from sqlcmd';
END TRY
BEGIN CATCH
    PRINT 'Using default values for script'
    :setvar envVar 'DefaultValue'
END CATCH;