Data update

Task/Create-a-two-dimensional-array-at-runtime/DuckDB/create-a-two-dimensional-array-at-runtime.duckdb

@@ -0,0 +1,38 @@
+# Create an unnamed m*n array as a table with m rows, each row being a list
+create or replace function matrix(m, n, init) as table (
+  with recursive row as (
+    select list_transform(range(0,n), x -> z) as row
+    from (select init as z)),
+  cte as (
+    select 1 as i, row from row
+    union all
+    select i+1, row
+    from cte
+    where i < m
+  )
+  from cte
+);
+
+# The backing table
+create or replace table t_ (
+  i INTEGER NOT NULL check(i>0), check(i<= getenv('M')::INTEGER),
+  row DOUBLE[]
+);
+
+# The view
+create or replace view t as from t_ order by i;
+
+# Initialize the backing table
+insert into t_ from matrix( getvariable('M')::INT, getvariable('N')::INT, 0.0);
+
+prepare update_matrix as /* $1=i $2=j $3=value */
+update t_
+  set row = row[1:$2-1] || [$3] || row[$2+1:]
+  where i =  $1
+;
+
+create or replace function matrix_get(ii,jj) as (
+  select row[jj]
+  from t
+  where i = ii
+  );