SQL Server: Concatenating Multiple Rows into a Single Delimited Field - Two Efficient Methods

This is the recommended method for newer versions of SQL Server as it's more concise and efficient. STRING_AGG aggregates values from multiple rows into a single string, allowing you to specify a separator between each value.

Here's an example:

CREATE FUNCTION dbo.ConcatValues (@table table_name, @id_column varchar(max), @value_column varchar(max), @separator varchar(max) = ',')
RETURNS VARCHAR(MAX)
AS
BEGIN
  DECLARE @result VARCHAR(MAX) = '';

  SELECT @result = STRING_AGG(@value_column, @separator)
  FROM @table
  WHERE @id_column = id;

  RETURN @result;
END;

This function takes four parameters:

• @table: The name of the table containing the data.
• @id_column: The column containing the ID used for grouping.
• @value_column: The column containing the values to concatenate.
• @separator (optional): The separator to use between concatenated values (defaults to comma).

This method uses the FOR XML PATH clause to convert the subquery results into an XML string and then extracts the desired values.

CREATE FUNCTION dbo.ConcatValues (@table table_name, @id_column varchar(max), @value_column varchar(max), @separator varchar(max) = ',')
RETURNS VARCHAR(MAX)
AS
BEGIN
  DECLARE @result VARCHAR(MAX) = '';

  SELECT @result = STUFF((
    SELECT @separator + @value_column
    FROM @table
    WHERE @id_column = id
    FOR XML PATH('')
  ), 1, 1, '');

  RETURN REPLACE(@result, @separator, '');
END;

This function works similarly to the previous one, but it achieves concatenation using XML manipulation.

Learning Italian in 12 Weeks:

While creating SQL functions is a valuable skill, learning a new language like Italian requires a different approach. Here's a possible 12-week study plan to get you started:

Weeks 1-4:

• Focus on building a strong foundation in Italian pronunciation and basic grammar.
• Utilize online resources like Duolingo or Memrise for interactive learning.
• Supplement your studies with audio lessons to improve listening comprehension.

• Gradually introduce more complex grammar structures and vocabulary.
• Read beginner-friendly Italian texts and listen to podcasts or audiobooks.
• Find a language exchange partner to practice conversation and gain fluency.

• Increase the difficulty of reading materials and focus on conversation practice.
• Immerse yourself in Italian culture through movies, music, and TV shows.
• Consider enrolling in an online Italian course for structured learning.

Remember, consistency is key. Dedicate at least 30 minutes to an hour daily to studying Italian.

Here are some additional tips:

• Set realistic goals and track your progress.
• Don't be afraid to make mistakes while speaking.
• Find ways to make learning fun and engaging.

Example Codes for SQL Server Functions (String Concatenation)

CREATE FUNCTION dbo.ConcatValues (
  @table table_name,
  @id_column varchar(max),
  @value_column varchar(max),
  @separator varchar(max) = ','
)
RETURNS VARCHAR(MAX)
AS
BEGIN
  DECLARE @result VARCHAR(MAX) = '';

  SELECT @result = STRING_AGG(@value_column, @separator)
  FROM @table
  WHERE @id_column = id;

  RETURN @result;
END;

CREATE FUNCTION dbo.ConcatValues (
  @table table_name,
  @id_column varchar(max),
  @value_column varchar(max),
  @separator varchar(max) = ','
)
RETURNS VARCHAR(MAX)
AS
BEGIN
  DECLARE @result VARCHAR(MAX) = '';

  SELECT @result = STUFF((
    SELECT @separator + @value_column
    FROM @table
    WHERE @id_column = id
    FOR XML PATH('')
  ), 1, 1, '');

  RETURN REPLACE(@result, @separator, '');
END;

This method iterates through the subquery results using a cursor and builds the concatenated string incrementally. While less efficient than the previous methods, it can be useful for understanding the process.

CREATE FUNCTION dbo.ConcatValues (
  @table table_name,
  @id_column varchar(max),
  @value_column varchar(max),
  @separator varchar(max) = ','
)
RETURNS VARCHAR(MAX)
AS
BEGIN
  DECLARE @result VARCHAR(MAX) = '';
  DECLARE @cur CURSOR FOR
  SELECT @value_column
  FROM @table
  WHERE @id_column = id;

  DECLARE @val VARCHAR(MAX);

  OPEN @cur;
  FETCH NEXT FROM @cur INTO @val;

  WHILE @@FETCH_STATUS = 0
  BEGIN
    SET @result = ISNULL(@result, '') + @val + @separator;
    FETCH NEXT FROM @cur INTO @val;
  END;

  CLOSE @cur;
  DEALLOCATE @cur;

  SET @result = LEFT(@result, LEN(@result) - LEN(@separator));

  RETURN @result;
END;

This function uses a cursor to loop through each value in the subquery. It builds the string by adding each value with a separator and then removes the trailing separator at the end.

Using WHILE loop with subquery:

This method utilizes a WHILE loop that repeatedly executes a subquery until no more rows are found. It then concatenates the retrieved value within the loop.

CREATE FUNCTION dbo.ConcatValues (
  @table table_name,
  @id_column varchar(max),
  @value_column varchar(max),
  @separator varchar(max) = ','
)
RETURNS VARCHAR(MAX)
AS
BEGIN
  DECLARE @result VARCHAR(MAX) = '';
  DECLARE @val VARCHAR(MAX);

  SET @val = (
    SELECT TOP 1 @value_column
    FROM @table
    WHERE @id_column = id
    ORDER BY id
  );

  WHILE @val IS NOT NULL
  BEGIN
    SET @result = ISNULL(@result, '') + @val + @separator;
    SET @val = (
      SELECT TOP 1 @value_column
      FROM @table
      WHERE @id_column = id
      AND id > (SELECT id FROM @table WHERE @value_column = @val)
      ORDER BY id
    );
  END;

  SET @result = LEFT(@result, LEN(@result) - LEN(@separator));

  RETURN @result;
END;

This function uses a WHILE loop with a subquery inside. The subquery retrieves the next value based on the ID, ensuring it doesn't pick the same value twice. It concatenates the retrieved value with the separator and continues looping until there are no more rows.