How to use regex to extract text in order?

Question

I am working on a python flow script. Which basically parses SQL statements and get the target table and the source tables. Example

CREATE TABLE TAR_TAB1 AS
SELECT * FROM SRC_TAB1 JOIN SRC_TAB2

CREATE TABLE TAR_TAB2 AS 
SELECT * FROM SRC_TAB3 JOIN SRC_TAB4

INSERT INTO TAR_TAB3 AS
SELECT * FROM SRC_TAB5 JOIN SRC_TAB6

I wrote regex

target = re.findall(r'\w+(?=\s+AS)', data)
source = re.findall(r'(?:FROM|JOIN)\s*([^\s]+), data)

the results are as expected,

target list contains, TAR_TAB1, TAR_TAB2, TAR_TAB3
source list contains, SRC_TAB1, SRC_TAB2, SRC_TAB3, SRC_TAB4, ETC

HOW TO GET OUTPUT LIKE EITHER LIST OR DATA FRAME LIKE, preferably dataframe, as such the flow of extraction is not disturbed.

target         source
TAR_TAB1       SRC_TAB1
TAR_TAB1       SRC_TAB2
TAR_TAB2       SRC_TAB3
TAR_TAB2       SRC_TAB4
TAR_TAB3       SRC_TAB5
TAR_TAB4       SRC_TAB6

Answer 1

Here's a solution:

targets = re.findall(r'(?:CREATE\s+TABLE|INSERT\s+INTO)\s+([a-z0-9A-Z_]+)\s+AS', text)
sources = re.findall(r'SELECT\s+\*\s+FROM\s([a-z0-9A-Z_]+)\s+JOIN\s+([a-z0-9A-Z_]+)', text)

# each target has multiple sources, so repeat each target n times per 
# number of sources.
lens = [len(src) for src in sources]
targets = np.repeat(targets, lens) 

# 'flatten' the list of sources from [(t1, t2), (t3, t4)] to 
# [t1, t2, t3, t4]
sources = [tab for exp in sources for tab in exp]

pd.DataFrame({"src": sources, "tgt": targets})

Results:

        src       tgt
0  SRC_TAB1  TAR_TAB1
1  SRC_TAB2  TAR_TAB1
2  SRC_TAB3  TAR_TAB2
3  SRC_TAB4  TAR_TAB2
4  SRC_TAB5  TAR_TAB3
5  SRC_TAB6  TAR_TAB3