value substitution/replacement in a string - sql

Question

I have a string x-y+z. The values for x, y and z will be stored in a table. Say
x 10
y 15
z 20
This string needs to be changed like 10-15+20.
Anyway I can achieve this using plsql or sql?

Answer 1

using simple Pivot we can do
DECLARE #Table1 TABLE
( name varchar(1), amount int )
;
INSERT INTO #Table1
( name , amount )
VALUES
('x', 10),
('y', 15),
('Z', 25);
Script
Select CAST([X] AS VARCHAR) +'-'+CAST([Y] AS VARCHAR)+'+'+CAST([Z] AS VARCHAR) from (
select * from #Table1)T
PIVOT (MAX(amount) FOR name in ([X],[y],[z]))p

Answer 2

An approach could be the following, assuming a table like this:
create table stringToNumbers(str varchar2(16), num number);
insert into stringToNumbers values ('x', 10);
insert into stringToNumbers values ('y', 20);
insert into stringToNumbers values ('zz', 30);
insert into stringToNumbers values ('w', 40);
First tokenize your input string with something like this:
SQL> with test as (select 'x+y-zz+w' as string from dual)
2 SELECT 'operand' as typ, level as lev, regexp_substr(string, '[+-]+', 1, level) as token
3 FROM test
4 CONNECT BY regexp_instr(string, '[a-z]+', 1, level+1) > 0
5 UNION ALL
6 SELECT 'value', level, regexp_substr(string, '[^+-]+', 1, level) as token
7 FROM test
8 CONNECT BY regexp_instr(string, '[+-]', 1, level - 1) > 0
9 order by lev asc, typ desc;
TYP LEV TOKEN
------- ---------- --------------------------------
value 1 x
operand 1 +
value 2 y
operand 2 -
value 3 zz
operand 3 +
value 4 w
In the example I used lowercase literals and only +/- signs; you can easily edit it to handle something more complex; also, I assume the input string is well-formed.
Then you can join your decoding table to the tokenized string, building the concatenation:
SQL> select listagg(nvl(to_char(num), token)) within group (order by lev asc, typ desc)
2 from (
3 with test as (select 'x+y-zz+w' as string from dual)
4 SELECT 'operand' as typ, level as lev, regexp_substr(string, '[+-]+', 1, level) as token
5 FROM test
6 CONNECT BY regexp_instr(string, '[a-z]+', 1, level+1) > 0
7 UNION ALL
8 SELECT 'value', level, regexp_substr(string, '[^+-]+', 1, level) as token
9 FROM test
10 CONNECT BY regexp_instr(string, '[+-]', 1, level - 1) > 0
11 order by lev asc, typ desc
12 ) tokens
13 LEFT OUTER JOIN stringToNumbers on (str = token);
LISTAGG(NVL(TO_CHAR(NUM),TOKEN))WITHINGROUP(ORDERBYLEVASC,TYPDESC)
--------------------------------------------------------------------------------
10+20-30+40
This assumes that every literal in you input string has a corrensponding value in table. You can even handle the case of strings with no corrensponding number, for example assigning 0:
SQL> select listagg(
2 case
3 when typ = 'operand' then token
4 else to_char(nvl(num, 0))
5 end
6 ) within group (order by lev asc, typ desc)
7 from (
8 with test as (select 'x+y-zz+w-UNKNOWN' as string from dual)
9 SELECT
.. ...
16 ) tokens
17 LEFT OUTER JOIN stringToNumbers on (str = token);
LISTAGG(CASEWHENTYP='OPERAND'THENTOKENELSETO_CHAR(NVL(NUM,0))END)WITHINGROUP(ORD
--------------------------------------------------------------------------------
10+20-30+40-0

Answer 3

Create a function like this:
create table ttt1
( name varchar(1), amount int )
;
INSERT INTO ttt1 VALUES ('x', 10);
INSERT INTO ttt1 VALUES ('y', 15);
INSERT INTO ttt1 VALUES ('z', 25);
CREATE OR REPLACE FUNCTION replace_vars (in_formula VARCHAR2)
RETURN VARCHAR2
IS
f VARCHAR2 (2000) := UPPER (in_formula);
BEGIN
FOR c1 IN ( SELECT UPPER (name) name, amount
FROM ttt1
ORDER BY name DESC)
LOOP
f := REPLACE (f, c1.name, c1.amount);
END LOOP;
return f;
END;
select replace_vars('x-y+z') from dual

Answer 4

Here's another way to approach the problem that attempts to do it all in SQL. While not necessarily the most flexible or fastest, maybe you can get some ideas from another way to approach the problem. It also shows a way to execute the final formula to get the answer. See the comments below.
Assumes all variables are present in the variable table.
-- First build the table that holds the values. You won't need to do
-- this if you already have them in a table.
with val_tbl(x, y, z) as (
select '10', '15', '20' from dual
),
-- Table to hold the formula.
formula_tbl(formula) as (
select 'x-y+z' from dual
),
-- This table is built from a query that reads the formula a character at a time.
-- When a variable is found using the case statement, it is queried in the value
-- table and it's value is returned. Otherwise the operator is returned. This
-- results in a row for each character in the formula.
new_formula_tbl(id, new_formula) as (
select level, case regexp_substr(formula, '(.|$)', 1, level, NULL, 1)
when 'x' then
(select x from val_tbl)
when 'y' then
(select y from val_tbl)
when 'z' then
(select z from val_tbl)
else regexp_substr(formula, '(.|$)', 1, level, NULL, 1)
end
from formula_tbl
connect by level <= regexp_count(formula, '.')
)
-- select id, new_formula from new_formula_tbl;
-- This puts the rows back into a single string. Order by id (level) to keep operands
-- and operators in the right order.
select listagg(new_formula) within group (order by id) formula
from new_formula_tbl;
FORMULA
----------
10-15+20
Additionally you can get the result of the formula by passing the listagg() call to the following xmlquery() function:
select xmlquery(replace( listagg(new_formula) within group (order by id), '/', ' div ')
returning content).getNumberVal() as result
from new_formula_tbl;
RESULT
----------
15