Data commit

Task/Run-length-encoding/SQL/run-length-encoding-1.sql

@@ -0,0 +1,47 @@
+-- variable table
+drop table if exists var;
+create temp table var (	value varchar(1000) );
+insert into var(value) select 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW';
+
+-- select
+with recursive
+ints(num) as
+(
+	select 1
+	union all
+	select num+1
+	from ints
+	where num+1 <= length((select value from var))
+)
+,
+chars(num,chr,nextChr,isGroupEnd) as
+(
+	select tmp.*, case when tmp.nextChr <> tmp.chr then 1 else 0 end groupEnds
+	from (
+	select num,
+		   substring((select value from var), num, 1) chr,
+		   (select substring((select value from var), num+1, 1)) nextChr
+	from ints
+	) tmp
+)
+select (select value from var) plain_text, (
+	select string_agg(concat(cast(maxNoWithinGroup as varchar(10)) , chr), '' order by num)
+	from (
+		select *, max(noWithinGroup) over (partition by chr, groupNo) maxNoWithinGroup
+		from (
+			select	num,
+					chr,
+					groupNo,
+					row_number() over( partition by chr, groupNo order by num) noWithinGroup
+			from (
+			select *, (select count(*)
+					   from chars chars2
+					   where chars2.isGroupEnd = 1 and
+					   chars2.chr = chars.chr and
+					   chars2.num < chars.num) groupNo
+			from chars
+			) tmp
+		) sub
+	) final
+	where noWithinGroup = 1
+	) Rle_Compressed