How (from where) to read SQL queries?

Question

SQL

I ran into a problem that even my requests that I wrote for a long time, I remember for a long time what they did.
Let's say there is a request for 200-300 lines with genies, groupings, and so on.
How to read them quickly and correctly?
Ie, something like a piece that painted blocks that should be read first, second, etc.
Ie, let's say we read books from left to right
. And SQL?

Answer 1

Let's say there is a request for 200-300 lines with genies, groupings, and so on.

Do the same as with the source code of programs: break into smaller pieces using views (view) and calculated fields in tables. For example, a complex search can be divided into 2 views: for the search and the result (the query itself will be short):

Search Grid

SELECT DISTINCT
         SearchName.ID, 
         SearchName.[Year], 
         SearchName.[Name], 
         SearchName.WatchDisplay, 
         SearchName.Icon,
         SearchName.AttributeIcon,
         SearchName.[Range],
         LEFT(SearchName.[Key], 1) AS Kind,
         SearchName.UnitID
    FROM SearchName INNER JOIN SearchLike ON SearchName.[Key] = SearchLike.[Key]
    WHERE ((NOT @P1 IS NULL) AND (SearchLike.Search LIKE '%' + @P1 + '%'))
       OR ((NOT @P2 IS NULL) AND (SearchLike.Search LIKE '%' + @P2 + '%')) 
       OR ((NOT @P3 IS NULL) AND (SearchLike.Search LIKE '%' + @P3 + '%')) 
    ORDER BY SearchName.[Range]

Using views:

SearchLike

CREATE VIEW SearchLike
AS
  SELECT Film.ID, 
         ISNULL(CAST(Film.Year AS VARCHAR) + ' ', '') + ISNULL(Head.Name + ' ' + Film.HeadingNumber + ' ', '') 
           + ISNULL(Film.Article + ' ', '') + ISNULL(Film.Name + ' ', '') + ISNULL(Film.NameTranslat + ' ', '') 
           + ISNULL(Film.Addition + ' ', '') + ISNULL(Film.Country + ' ', '') 
           + ISNULL(FilmAttributeGroup.Name + ' ', '') + ISNULL(FilmAttributeValue.Value + ' ', '') AS Search,
         Film.[Key]
    FROM FilmAttributeValue 
      INNER JOIN FilmAttribute ON FilmAttributeValue.ID = FilmAttribute.Attribute 
      INNER JOIN FilmAttributeGroup ON FilmAttributeValue.[Group] = FilmAttributeGroup.ID 
      RIGHT OUTER JOIN Film ON FilmAttribute.Film = Film.ID 
      LEFT OUTER JOIN Film AS Head ON Film.Heading = Head.ID
  --
  UNION
  --
  SELECT Person, 
         [Name], 
         'P' + CAST(Person AS VARCHAR)
    FROM PersonNameFormat
    WHERE ([Format] > 10) OR ([Format] = 0)
--
GO

SearchName

CREATE VIEW SearchName
AS
  -- Фильмы:
  SELECT Film.ID, 
         FilmNamePower.[Year]     AS [Year], 
         FilmNamePower.NameCommon AS [Name], 
         Film.WatchDisplay,
         Film.Icon,
         Film.AttributeIcon,
         '0' + Film.[Range] AS [Range],
         Film.[Key],
         Film.ID AS UnitID
    FROM Film INNER JOIN FilmNamePower ON Film.ID = FilmNamePower.ID
  --
  UNION
  -- Персоны:
  SELECT ID, 
         ISNULL(YEAR(BirthDay), 1900), 
         NameFull, 
         '', 
         NoteIcon, 
         NULL, 
         '1' + CONVERT(VARCHAR, ISNULL(BirthDay, '19000101'), 112) + [Range], 
         [Key],
         -1
    FROM Person

The latter uses a view:

FilmNamePower

CREATE VIEW FilmNamePower
AS
  -- Фильмы:
  SELECT Film.ID,
         Film.[Range],  
         Film.[Range]               AS [RangeSort],  
         ISNULL(Film.[Year], 1895)  AS [Year], 
         Film.TitleCountry          AS NameCommon,
         Film.TitleYearCountry      AS NameYearCountry,
         Film.TitleBase             AS NameBase,
         Film.SearchValue,
         Film.Icon,
         Film.AttributeIcon,
         Film.LastWatch,
         Film.WatchDisplay,
         Film.ID                    AS IDCover
    FROM Film
    WHERE (Heading IS NULL)
  -- Многосерийные фильмы и сериалы:
  UNION
  --
  SELECT Film.ID, 
         Head.[Range] + Film.[Range],  
         Film.[Range],
         ISNULL( ISNULL(Film.[Year], Head.[Year]), 1895), 
         ISNULL(CAST(Head.HeadingName AS VARCHAR(200)), Head.Name) + IIF(Film.HeadingNumber = '','',', ' + Film.HeadingNumber) 
                                                          + IIF((Film.TitleBase IS NULL),'' + Film.PartDisplay, ': ' + Film.TitleBase )
                                                          + ISNULL( ' · ' + ISNULL( Film.Country, Head.Country), ''), 
         ISNULL(CAST(Head.HeadingName AS VARCHAR(200)), Head.Name) 
           + ', ' + Film.HeadingNumber +  
                             + IIF( (Film.TitleBase IS NULL), 
                                                 Film.PartDisplay + ' · ' + CAST(ISNULL( ISNULL(Film.[Year], Head.[Year]), 1895) AS VARCHAR),
                                                ': ' + Film.[TitleYear] )
                             + ISNULL( ' · ' + ISNULL( Film.Country, Head.Country), ''),
         ISNULL(CAST(Head.HeadingName AS VARCHAR(200)), Head.Name) + IIF(Film.HeadingNumber = '','',', ' + Film.HeadingNumber) 
                                                          + IIF((Film.TitleBase IS NULL),'' + Film.PartDisplay, ': ' + Film.TitleBase ), 
         Head.SearchValue + ISNULL('+s' + RIGHT('00' + CONVERT([varchar], Film.Season), 2), ''),
         Film.Icon,
         Film.AttributeIcon,
         Film.LastWatch,
         Film.WatchDisplay,
         Head.ID
    FROM Film 
      INNER JOIN Film AS Head ON Film.Heading = Head.ID 
    WHERE NOT (Film.Heading IS NULL)
--
GO

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Answer 2

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